# Sum of N numbers in C using For loop

Before we move on the program of sum of N numbers, first we have to know about the For Loop statement.

The syntax of ‘for’ loop in C programming language is given below:

``````for (initialization statement; test expression; update statement)
{
/* main body of the ‘for’ loop */
}
``````

How does the ‘for’ loop work?

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.

The following program sum up all the ‘n’ numbers entered by the user with the help of For loop in ‘C’ programming language:

``````#include<stdio.h>
int main() {
int n, a = 0, b; /* declaring various variables and initialization the value of 'a' as 0 */
printf("Enter the amount of natural numbers you want to add: \n");
/* here we let user to enter a number via this program line */
scanf("%d", &n);
/* assigning the value entered by the user to variable 'n' */
printf("Enter any %d numbers that you want to add: \n" , n);
/* here we let user to enter an number via this program line */
for (int z = 1; z<=n; z++)
/* for (initialization statement; test expression or termination condition; increment or decrement statement) */
{
scanf("%d" , &b);
/* assigning the value entered by the user to variable 'b' */
a = a + b;
/* initializing assignment operator and assigning the value a + i to a */
}
printf("Sum of the natural numbers you entered is: %d", a);
/* printing the value of result as an output */
return 0;
}
``````

Output:

``````Enter the amount of natural numbers you want to add:
5
Enter any 5 numbers that you want to add:
2
3
4
5
6
Sum of the natural numbers you entered is: 20
``````

Explanation:

Initially, we have declared three variables n, a, and b. And, we initialized the value of variable ‘a’ as 0, it means that we can avoid the value of variable ‘a’ from going into negative.

Then, we used the scanf statement which allows the user to enter an input in n variable on the output console. The variable ‘n’ shows the total amount of numbers we want to add.

In the below line we define the ‘for’ loop that includes three components first is an initialization statement that includes the initialization of a variable as here we declared variable ‘z’ and its initial value was set to 1.

Second is a test expression or a termination condition (z<=n) that specify the value of variable ‘z’ must be less than or equal to value of variable ‘n’.

Third is an increment statement that helps in altering or modifying the value of variable ‘z’ after each iteration of loop.

Now, we used a ‘scanf’ command which enter the value of variable b.

In the next statement, we specified the addition arithmetic operation for adding the value of variable ‘a’ and ‘b’. And, assign the sum to the variable ‘a’. At last we wrote a ‘printf’ statement to print the last value of variable ‘a’ after the loop termination.