Loop Questions in C

Question 1: What is For loop syntax?

Ans:

The syntax that has been used for the ‘for’ loop in C programming language is:

for (initialization statement /*for providing a value to variables*/; test expression /*to terminate a specified condition*/; update statement /*modify statement for further evaluation*/)
{
    /* main body of the ‘for’ loop */
}

Question 2: How does the for loop work?

Ans:

In for loop, the initialization command is implemented only once.

After that, it checks the test expression of the loop and finds whether the test expression is false or true. And, for loop is dismissed if the test expression is false.   
If the test expression of the 'F' loop becomes true, then the program line provided in the F loop’s body is executed, and the update expression is changed accordingly.
Again, the entire process of evaluation is to be done. The loop executes its body until and unless the value of the test expression in for loop becomes false. The loop automatically terminates as soon as the test expression result becomes false.

Question 3: What is while loop syntax?

Ans.

The syntax that can be used for the “while” loop in the C programming language is following:

while (test expression or termination condition (to terminate at specified condition)) 
{// the main body of the ‘while’ loop is written here}

Here we will let you know about the working of the “while” loop in C programming:

Initially, we use the parentheses for storing the termination condition of the While loop. Then, there can be two outcomes True or False.

Firstly, if the result is true, then the control will automatically execute the body of the loop. It will continue to evaluate again and again until the termination condition is false. Secondly, if the result is false, then the control will definitely come out of the While loop and will dismiss the While Loop.

Question 4: What is do while loop syntax?

Ans:

do 
{
  /* main body used for the loop */
}
while (termination condition (to terminate at specified condition));

while (termination condition (to terminate at specified condition));

Working of a do-while loop in C:

Initially, the body of do-while executes only one time. After that, the control executes the termination condition.

It then checks whether the termination command results in true. If yes, it will print the desired outcome on the screen, and it will continue to execute the termination condition again and again. One more thing is that the execution will run multiple times until the condition become false.
As soon as the results become false after the execution of the termination command, then the loop will be automatically dismissed.

Question 5: What is nested loop?

Ans:

A nested loop is generally used when we want to run a loop statement inside another loop statement. This kind of loop is also known as a “loop inside the loop”.

Explanation of execution of Nested loop:

In the nested loop, first we provide an initialization statement. Then, the control evaluates the value of the first condition and checks whether the termination condition is true or false.
If the value is false, it will terminate the entire process and only perform the basic command. But if the value is true, it will continue to check the second condition. If it finds the second condition false, it will terminate the processing of the program of the second condition and move to the primary/first loop and perform it.

And, if the second condition results to true, control will execute the loop and termination condition repeatedly until the value of condition becomes false. Along with this, some increment or decrement statements are implemented after every loop execution.

As the second condition terminates, it goes back to the first condition, checks again, and repeats the entire execution process. The execution of termination condition can take place multiple times. According to the loop, C control performs the condition given at the end and produces the outcome. At last, it will display the output on the screen.

Question 6: What is nested for loop syntax?

Ans:

Syntax used in initiating nested For loop:

for (initialization statement (for providing a value to variables); test expression (to terminate at specified condition); update statement (modify statement for further evaluation))
 {
      // initialization of the first for loop
   }
   // initialization of the second for loop
}

Question 7: What is nested while loop syntax?

Ans:

Syntax Used for Initiating Nested While Loop:

while (test expression (to terminate at specified condition)) 
{
// condition must be provided 
   while (test expression (to terminate at specified condition)) 
   { 
      // initialization of the first while loop
   }
   // initialization of the second while loop
}

Question 8: What is nested do while loop syntax?

Ans:

Syntax Used for Initiating Nested Do-While Loop:

do
{
   do
   {     
      // initialization of the first do while loop
   }
while(test expression (to terminate at specified condition)); //condition is given here
   // initialization of the second do while loop
}
while(test expression (to terminate at specified condition));

Question 9: What is nested mixed loop syntax?

Ans:

Syntax Used for Initiating Nested Mixed (Do-While, While, For) Loop:

do
{while(test expression (to terminate at specified condition)) 
// condition should be provided
{   
 for (initialization statement (for providing a value to variables); test expression (to terminate at specified condition); update statement (modify statement for further evaluation))
 
{// initialization of the first loop
 }
  // initialization of the first while loop
 }
 // initialization of second do-while loop
}
while(test expression (to terminate at specified condition));

Question 10: What is an infinity loop?

Ans:

The infinite loop is that loop which does not get dismissed because of its looping construct. A continuous output or no output are the two possible outcomes of this loop. It is also known as an endless loop or an indefinite loop.

There are a lot of applications where an infinite loop is helpful in running applications continuously. Those applications also produce endless outputs until the process is terminated manually. A few of them are the following:

1. Games: The user can play unlimited matches continuously, but if the user wants to stop the match, the h/.she has to exit the game manually. The game does not terminate on its own.
2. Operating Systems: As we usually observe, any operating system does not terminate their functioning on their own after the completion of task, until and unless the user manually shut downs the system.
3. Servers and website: Infinite loop is also used in servers and websites which produce the output as many times the user asks to carry out the process. This processing only gets dismissed when the user closes the website or when the administrator manually shuts the servers and websites down.

Question 11: Write an example of infinite ‘for’ loop.

Ans:

#include <stdio.h>
int main ()  
{  
    int a, b=3; /* declaration and initialization of variables */ 
   for (a=2; a<=b; a--)  
/*for (initialization statement (for providing a value to variables); test expression (to terminate at specified condition); update statement (modify statement for further evaluation)) */
   {   
     printf ("tutorial and example\t"); // printing the output
   }  
return 0;  
} 

Output:

tutorial and example    tutorial and example	    tutorial and example     tutorial and example    tutorial and example    tutorial and example     tutorial and example    tutorial and example    tutorial and example     tutorial and example    tutorial and example    tutorial and example     tutorial and example    tutorial and example    tutorial and example     tutorial and example    tutorial and example    tutorial and example     tutorial and example

Question 12: Write an example of infinite ‘while’ loop.

Ans:

// basic program lines 
#include <stdio.h>  
int main ()  
{  
  int a=1; 
  /* declaration and initialization of variables */  
  while (1)
  {  
      a++;   
      /* increment or decrement statement */ 
      printf("Now a's value is:%d \t", a);  
      /* printing output */
  }  
return 0;  
}  

Output:

Now a's value is:2      Now a's value is:3      Now a's value is:4        Now a's value is:5       Now a's value is:6      Now a's value is:7      Now a's value is:8       Now a's value is:9      Now a's value is:10     Now a's value is:11     Now a's value is:12     Now a's value is:13    Now a's value is:14      Now a's value is:15     Now a's value is:16    Now a's value is:17     Now a's value is:18     Now a's value is:19     Now a's value is:20      Now a's value is:21      Now a's value is:22      Now a's value is:23      Now a's value is:24     Now a's value is:25    Now a's value is:26      Now a's value is:27     Now a's value is:28      Now a's value is:29      Now a's value is:30

Question 13: Write an example of infinite ‘do while’ loop.

Ans:

#include <stdio.h> 
int main ()
{
do  
{  
   printf("All the way up "); 
   /* initializing main body of the infinite do while loop.. */  
}
while (1); /* 1 is considered as true and 0 as false */
}

Output:

All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way up All the way

Question 14: What is the difference between ‘while’ loop and ‘do while’ loop?

Ans:

While loop:

Initially, we use the parentheses for storing the termination condition of the While loop. Then, there can be two outcomes True or False.

Firstly, if the result is true, then the control will automatically execute the body of the loop. It will continue to evaluate again and again until the termination condition is false. Secondly, if the result is false, then the control will definitely come out of the While loop and will dismiss the While Loop.

Do-while loop in C:

Initially, the body of do-while executes only one time. After that, the control executes the termination condition.

It then checks whether the termination command results in true. If yes, it will print the desired outcome on the screen, and it will continue to execute the termination condition again and again. One more thing is that the execution will run multiple times until the condition become false.
As soon as the results become false after the execution of the termination command, then the loop will be automatically dismissed.

Question 15: What is ‘entry’ control loop in C programming language?

Ans:

Initially, an entry control loop verifies the termination condition at the entry point. After that, its control passes to the main body of the while or for loop if the termination condition or test expression becomes true. This kind of loop usually regulates the ‘while’ and ‘for’ loop entrance. Due to this, it is known as an entry control loop in C.

Question 16: What is ‘exit’ control loop in C programming language?

Ans:

To examine the termination condition for exit, we usually use an exit control loop in C.

If the evaluation for termination condition results in true, then the control would be exited from the main body of the loop. Otherwise, the control enters inside the loop one more time.

This sort of loop usually deals with the exit control statement of the loop.

Question 17: How to print for factorial of any number using ‘for’ loop?

Ans:

Factorial of any positive integer:

#include <stdio.h>
int main () 
{
    int n, a; // declaring variables  
    unsigned long long fact = 1;
    printf ("Enter any positive number: \n"); // taking input from the user
    scanf ("%d", &n); // assigning the value inputted by the user to the declared variable
    // program line in case the user enters a negative integer, it will display error
    if (n < 0) // if termination condition
        printf ("Error 404! Sorry to say but there is no factorial of a negative integer."); // to display error
    else {
        for (a = 1; a <= n; ++a) // (initialization statement, test expression, increment statement) 
{
            fact *=a;
        }
        printf ("The factorial of given number is %d = %llu", n, fact); // printing output
    }
    return 0;
} 

This program will take a positive integer as an input from the user and compute the factorial of the given number with the help of for loop.

Sometimes, the factorial of some positive integers can be extremely large that’s why the “unsigned long long” is used as the data type of factorial variable to overcome this issue.

Suppose, the user enters any negative integer, the program will automatically display a pre-defined error message like this:

"Error 404! Sorry to say but there is no factorial of a negative integer"

Question 18: How to print for factorial of any number using ‘while’ loop?

Ans:

 #include<stdio.h>
int main()
{
int a, b=1, c=1; // declaring various variables and initializing values of b and c as 1, 1 simultaneously  
printf("Enter the natural number whose factorial you want to print:\n"); // taking a value as input from the user 
scanf("%d", &a); // assigning the value entered by the user to a
// providing termination condition so that we can avoid loop from running to infinity     
while(b<=a) // initializing loop for calculating the factorial of a positive integer provided by the user as an input
{
        c=c*b; // main body of the while loop that is to be executed until it the loop gets terminated because of the false value retained by the execution of termination condition
        b++;
}
    printf("The factorial of the given number %d is as follow %d", a, c); // printing the output
return 0;
}

Initially, the system will let the user to enter any positive integer and assign the entered number to the variable ‘a’.
After that, the code will multiply the values of ‘b’ with the value of ‘c’ with the help of ‘while’ loop.  This ‘while’ loop will execute the multiplication until the value of ‘b’ does not equal to the value of ‘a’.
And, at last, the program will automatically print the factorial value of the given number after the termination of while loop.

Question 19: How to print Fibonacci series using ‘for’ loop?

Ans:

#include <stdio.h>
int main () 
{
  int a, b;
  // declaring variables and initializing first and second terms without value
  int c1 = 0, c2 = 1; // declaring the value of term 1 as c1 = 0 and term 2 as c2 = 1 
  // initializing the upcoming third term (up.t.term) 
  int uptterm= t1 + t2;
  printf("Enter the no. of terms of the Fibonacci series you want to print: "); // taking input from the user about the no. of terms user wants to print
  scanf("%d", &b); // assigning the value entered by the user to b
  printf("Fibonacci Series is as follow: %d, %d, ", c1, c2); // printing the values of the first two declared as terms c1 and c2
  for (a = 3; a <= n; ++a) // (initialization statement; termination condition; increment or decrement statement) 
// printing the 3rd term and to the nth terms 
{
    printf("%d, ", uptterm);
    c1 = c2;
    c2 = uptterm;
    uptterm = c1 + c2;
  }
  return 0;
}

Question 20: How to print Fibonacci series using ‘while’ loop?

Ans:

#include<stdio.h>
int main ()
{
    int a=0, b=1, c, x=3, terms; 
/* declaring variables and initializing values of all variables */
    printf ("Enter the no. of terms of the Fibonacci series you want to print: "); 
/* taking input from the user to print the result */
    scanf ("%d", &terms); 
/* assigning the value entered to the variable -'terms' */
    printf ("%d\t %d", a, b); 
/* program command to print the values of 'a' and 'b' */
    while(x<=terms) 
/* termination condition or test expression */           
    {
        c=b + a; 
/* using assignment operator to assign the sum total value of 'b' and 'a'to 'c' */    
        printf ("\t %d", c); 
/* printing the value of variable 'c' that is equivalent to (b=a) */      
        a=b; 
/* using assignment operator to assign the value of 'a' to the 'b' */
        b=c; 
/* using assignment operator to assign the value of 'b' to the 'c' */
        x=x+1; 
/* using assignment operator to assign the incremented value of 'x' to 'x' itself */
    }
    return 0;
}

Question 21: How to find out prime numbers using ‘for’ loop?

Ans:

#include <stdio.h>
int main() 
{
  int n, a, flag= 0; 
/* declaring variables and initiating the value of flag as 0 */
  printf("Enter any natural number:  \n"); /* taking input from the user */
  scanf("%d", &n); /* assigning the value entered by the user to variable “n” */
  /* note down, 0 and 1 are not considered as prime numbers */
  /* that’s why providing value 1 for non-prime number flags (as flag=1) */
  if (n == 0 || n == 1) /* using “or” operator and comparison operators */
    flag = 1; /* assigning value to non-prime flags */
  for (a = 2; a <= n / 2; ++a) /* (initialization statement; termination condition; increment or decrement statement) */
{
    /* here we are declaring the fact that if the value of “n” is divisible by the value of “a”, in that case, “n” cannot be considered as a prime number for non-prime numbers we are going to set the value of flag as 1 */
    if (n % a == 0) 
/* n % a here means the remainder, when you divide the value of “n” by “a” */
{
      flag =1;
      break; 
/* break statement for ending the loop execution here */
    }
  }
  if (flag == 0)
    printf("%d can be considered as a prime number.", n); 
/* printing output for first situation */
  else
    printf("%d cannot be considered as a prime number.", n); 
/* printing output for first situation */
  return 0;
}

Question 22: Write a program to find out the composite numbers upto the number entered by the user with the help of for loop.

Ans:

#include<stdio.h>
#include<math.h>
int main ()
{
    int a, b, c; // declaring various variables without assigning values
    printf("Input a natural number up to which you want to print composite numbers :"); // taking input from the user
    scanf("%d", &c); // assigning value entered by the user to c
    for (a=2; a<=c; a++) // (initialization statement; termination condition; increment/decrement statement)  
    {
        for (b=2; b<=(int) pow(a,0.5); b++) // (initialization statement; termination condition; increment/decrement statement)  
        {
            if(a%b==0) // initializing if statement
            {
                printf("%d can be considered as a composite number \n", a); // printing the output
                break; // break statement to terminate “for” loop
            }    
        }
    }
    return 0;
}

Output:

Input a natural number up to which you want to print composite numbers :20
4 can be considered as a composite number
6 can be considered as a composite number
8 can be considered as a composite number
9 can be considered as a composite number
10 can be considered as a composite number
12 can be considered as a composite number
14 can be considered as a composite number
15 can be considered as a composite number
16 can be considered as a composite number
18 can be considered as a composite number
20 can be considered as a composite number

Question 23: Print the following output with the help of nested ‘while’ loop:

1

1 2

1 2 3

1 2 3 4

1 2 3 4 5

Ans:

#include <stdio.h>
int main ()
{
    int a=1, b; // declaring various variables as well as initiating value of ‘a’ as 1
    while (a <= 5) // while (termination condition)
    {
        b=1; // initialization of the value of ‘b’ as 1
        while (b <= a) // while (termination condition)
        {
            printf ("%d ", b); // printing the value of ‘b’ as an output
            b++; // increment statement to modify the value of ‘b’ for further evaluation
        }
       printf ("\n"); // printing the next line command as an output to change the new print line
        a++; // increment statement to modify the value of ‘b’ for further evaluation
    }
    return 0;
}

Question 24: Write down a program that prints the values from -5 to 5 with the help of all possible loops.

Ans.

With the help of ‘for’ loop:

#include <stdio.h>
int main ()
{ 
int a; // declaring variable
for (a=-5; a<6; ++a) // for (initialization statement, test expression, increment statement (modifying for further evaluation))
{
printf (“%d”, a); // printing the result as an output
}
return 0;
}

Output:

the value of a is -5
the value of a is -4
the value of a is -3
the value of a is -2
the value of a is -2
the value of a is -1
the value of a is 0
the value of a is 1
the value of a is 2
the value of a is 3
the value of a is 4
the value of a is 5 

With the help of ‘while’ loop:

/* Printing integers from -5 to 5 */
#include <stdio.h>
int main () 
{
  int a = -5; // declaring and initializing the value of ‘a’ as -5
  while (a <= 5) // termination condition
  {
    printf ("the value of ‘a’ is %d\n", a); // body of the ‘while’ loop 
    ++a; // increment/ decrement statement
  }
  return 0;
}

Output:

the value of a is -5
the value of a is -4
the value of a is -3
the value of a is -2
the value of a is -2
the value of a is -1
the value of a is 0
the value of a is 1
the value of a is 2
the value of a is 3
the value of a is 4
the value of a is 5 

With the help of ‘do while’ loop:

#include <stdio.h>
int main() 
{
  int a=-5;
    do //execute the task without checking the condition only once
  {
      printf("the value of a is %d\n", a);
      a++;//increment statement
  }  
    while(a<=5); //this is termination condition
  return 0;
}

Output:

the value of a is -5
the value of a is -4
the value of a is -3
the value of a is -2
the value of a is -2
the value of a is -1
the value of a is 0
the value of a is 1
the value of a is 2
the value of a is 3
the value of a is 4
the value of a is 5 

Question 25: Write a Program to print the table of any positive integers. You have to write a code which allows the user to enter the positive number at the run time.

Ans.

With the help of nested ‘for’ loop:

#include "stdio.h"
#include "conio.h"
void main()
{
    int n, a, ans; // declaring variables
    printf("\n Enter No. to print Table: ");
    scanf("%d", &n); // assigning value to a entered by the user
    /* for(initialization condition, 
    termination condition, increment or decrement condition) */
    for(a = 1; a <=10 ; a++ )
    {
       ans = n * a;
       printf("\n  %d * %d = %d", n,a, ans) ;
    }
    getch();
}

Output:

Enter No. to print Table: 2
  2 * 1 = 2
  2 * 2 = 4
  2 * 3 = 6
  2 * 4 = 8
  2 * 5 = 10
  2 * 6 = 12
  2 * 7 = 14
  2 * 8 = 16
  2 * 9 = 18
  2 * 10 = 20

Question 26: Make a program that can take input from the user and evaluate and print the factorial(!) of the entered positive number.

Ans.

With the help of ‘for’ loop:

#include <stdio.h>
int main () 
{
    int n, a; // declaring variables  
    unsigned long long fact = 1;
    printf ("Enter any positive number: \n"); // taking input from the user
    scanf ("%d", &n); // assigning the value inputted by the user to the declared variable
    // program line in case the user enters a negative integer, it will display error
    if (n < 0) // if termination condition
        printf ("Error 404! Sorry to say but there is no factorial of a negative integer."); // to display error
    else {
        for (a = 1; a <= n; ++a) // (initialization statement, test expression, increment statement) 
{
            fact *=a;
        }
        printf ("The factorial of given number is %d = %llu", n, fact); // printing output
    }
    return 0;
}

Output:

Enter an integer: 15
Factorial of 15 = 1307674368000

With the help of ‘while’ loop:

#include<stdio.h>
int main()
{
int a, b=1, c=1; // declaring various variables and initializing values of b and c as 1, 1 simultaneously  
printf("Enter the natural number whose factorial you want to print:\n"); // taking a value as input from the user 
scanf("%d", &a); // assigning the value entered by the user to a
// providing termination condition so that we can avoid loop from running to infinity     
while(b<=a) // initializing loop for calculating the factorial of a positive integer provided by the user as an input
{
        c=c*b; // main body of the while loop that is to be executed until it the loop gets terminated because of the false value retained by the execution of termination condition
        b++;
}
    printf("The factorial of the given number %d is as follow %d", a, c); // printing the output
return 0;
}

Output:

Enter the natural number whose factorial you want to print:
5
The factorial of the given number 6 is as follow 720

Here are some more loop questions:

Question 27: What is the difference between ‘for’ loop and ‘while’ loop?

Question 28: Write a C program for calculating the total of any consecutive negative and positive integers which are taken at run time by user.

Question 29: Construct a program that can assign two numbers entered manually by the user through the keyboard to different variables and can calculate the value of one integer raised to the power of another.

Question 30: Write a loop program that lets the user to input a numeral and then display the that number in reverse. Suppose 6487 is a entered number and its reverse is 7846 which is to be shown in output.

Question 31: Make a program that can read all the integers provided as input by the user and print the addition of all the even and odd numbers side by side.

Question 32: Construct a program using a loop that can read the inputted number by the user and can differentiate between the prime and non-prime numbers. The code print as ‘Number is a prime number’ or ‘Number is not a prime number’.

Question 33: Write a program that can provide the HCF of two numbers provided by the user.

Question 34: Write a do-while loop that enables the user to input two numbers. Initially, both the numbers must be added, and the sum should be displayed as an output. The loop must have an option for the user regarding running the program one more time only if the user wants. If yes, then run the program again. If not, then it should terminate.

Question 35: Write a program to print the addition of all the numbers entered by the user as per the need.

Question 36: Make a program that can read the numbers provided by the user as an input and can distinguish between the greater and smaller numerals. The code must print as an output.

Question 37: Construct a loop program to print all Armstrong numbers that lie between 1 and 500. Armstrong numbers are those numbers in which the total of each digit’s power raised to 3 is the same as the number provided. For example, 153 = (1 * 1 * 1) + (5 * 5 * 5) + (3 * 3 * 3)

Question 38: For printing the Fibonacci series, write down a loop program of n terms where n is provided by the user as input.
For instance 0 1 1 2 3 5 8 13 24 .... as an output.

Question 39: In order to evaluate the total of the below-given series, where n is the input provided by the user.
Series- 1 + 1/2 + 1/3 + 1/4 + 1/5 +.....1/n 

Question 40: Write a program, where n is a positive integer and input by the user, to calculate the natural logarithm of 2 by summing up all the numbers of series up to n terms.
Series- 1 - 1/2 + 1/3 - 1/4 + 1/5 -... 1/n

Question 41: Make an interesting game of guessing the number that has been generated by the machine, and that lets the user guess what the exact number it is.
If the user guesses higher than the number generated, the program should print "less than guessed, next time better luck." And if the user guesses lower than it, the program should automatically display "more than guessed, keep trying." The program should repeat itself until the user guesses the number generated by the machine correctly.

Question 42: Write down a loop program to calculate sin x for an initiated value of “x”. The user should provide the value of “x” and a positive integer “n” as input. The program evaluate the value of “sin” of “x” with the help of the following series, and this evaluation should utilize all the terms provided in the below-given series up to the term involving x’s power raised to the n.
Series- sin x = x - x³/3! + x⁵/5! - x⁷/7! + x⁹/9! .....