C Tutorial

C Tutorial C Language Environment Setup Execution flow of C program C printf and Scanf C Data type C Token Variable in C Operators in C Comments in C Escape Sequence in C C – Storage Classes C Decision control statement Loop Statement in C Break, continue and goto statement in C Type Casting in C Function in C Recursion in C String in C C Array Pointer in C Dynamic memory allocation C –Structure Nested Structure in C Union in C File Handling in C C pre-processor Static Function In C Sizeof In C Selection Sort In C Scope Of Variables In C Runtime Vs Compile Time In C Random Access Lseek In C Queue Implementation In C Pseudo Code In C Prototype In C Pointer To Pointer In C Pointer Arithmetic In C Passing Array To Function In C Null Character In C Merge Sort In C Macros In C Library Functions In C Memory Leak In C Int In C Goto And Labels In C Fibonacci Series In C Fflush In C Derived Data Types In C Data Types In C Const Vs Volatile In C Character Set In C Character Class Tests In C Calloc In C C Pointers Arrays In C Include In C Clrscr In C C Vs Java String Literals In C Types Of Pointers In C Variables In C Volatile In C Why C Is A Middle Level Language Infix To Postfix Program In C Ceil function in C LCM of two numbers in C Quick sort in C Static in C function pointer as argument in C Top Array Keywords in C Add two numbers using the function in C Armstrong program in C using function Array, Declaring Arrays and Array Initialization Limitations of Inline Function in C Merge and Merge sort with example in C Do-While Loop in C For Loop in C While-Loop in C Difference between while and do-while loop in C Array Of Structures in C Data Structures And Algorithms in C Types Of Structures In C How to Avoid Structure Padding in C Use of Structure in C Do WHILE LOOP in C Programming Examples For Loop in C Programming Examples Entry Control Loop in C Exit control loop in C Infinite loop in C Nested loop in C pow() function in C String Handling functions in C Prime Number code in C Factorial Program in C using For Loop Factorial Program in C Using While Loop Fibonacci Series in C Using For Loop Fibonacci series in C using while loop Prime Number Program in C using for Loop While Loop in C programming examples Built-in functions in C Assert() Function C vs Java Strings Call Back Function in Embedded C Else If Ladder fgets() function Ftell() Function getc() function getch() function gets() function Heap Sort Nested if-else statement Pi() Function Positioning of file Write() function abs() function in C Attributes in C C program to find factorial of a number using Recursion Ferror() in c fopen() function in C Fibonacci series program in C using Recursion Formatted Input and output function in C Snake Game in C User Defined Functions in C Beep() function in C Cbrt() function in C Hook() function in C Isalnum() function in C C Program to find the Roots of a Quadratic Equation C Switch Statements Difference between rand() and srand() function in C Difference between while and for loop in C Doubly Linked list in C Example of Iteration in C How to use atoi() function in C How to use floor() function in C How to use sine() function in C How to use Typedef Struct in C Integer Promotions in C C Program Swap Numbers in cyclic order Using Call by Reference C Program to Find Largest Number Using Dynamic Memory Allocation C Program to Find the Largest Number using Ternary Operator C/C++ Program to Find the Size of int, float, double and char Find the Largest Three Distinct Elements in an Array using C/C++ Loop Questions in C Modulus on Negative Numbers in C Multiplication table program in C using For loop Nested Loops in C Programming Examples C Program for Mean and Median of an Unsorted Array Results of Comparison Operations in C and C++ Reverse a Stack using Recursion in C Simple hash() function in C strcat() Function in C Sum of N numbers in C using For loop Use of free() function in C Write a program that produces different results in C and C++ C Function Argument and Return Values Keywords in C Bank management system in C Calendar application in C Floor() Function in C Free() Function in C How to delete a file in C How to move a text in C Remove an element from an array in C Unformatted input() and output() function in C What are linker and loader in C fork() in C GCD program in C Branching Statements in C Comma Operator in C Control statement in C Double Specifier in C How to create a binary file in C Long int in C Palindrome Number in C Pure Virtual Function in C Run Time Polymorphism in C Types of Array in C Types of Function in C What is a buffer in C What is required in each C Program Associativity of Operators in C Bit Stuffing Program in C Actual and Formal Parameters Addition of two Numbers in C Advantages of function in C

Goto and Labels in C

Introduction

Goto in C:

The goto statement is known as the jump statement in C. The goto is used to transfer the control of a program to a predefined label. The goto statement has one more application, which is, for a particular condition it performs repeat operation on some part of the code.

Labels in C:

The Labels in C are used with goto and switch statements. It can be defined as an identifier which is required for the goto statement. It is required as an identifier to a location where the branch is to be made.

Syntax:

goto label;

Theory:

The awareness about “goto” and “labels'' is widely known to every programmer who has gone through the surface of C programming. It is used in C programming to perform the jump operation. By jump we mean, jump within a C function.

Note:  In C, the GCC (GNU Compiler Collection) provides an extension which is called “local labels”.

Goto Statement in C

The goto statement is known as the jump statement in C. The goto is used to transfer the control of a program to a predefined label. C offers the infinitely-abusable goto statement, and labels to branch to. This means that the label is required as an identifier to a location where the branch is to be made.

The goto statement is not necessary, and in general it is quite easy to write code without the use of this statement. But there are a few scenarios where goto may play a vital role and resolve the problems the user may face in those conditions.

The most common scenario is to abandon processing in some deeply nested structure, such as breaking out of two or more loops at once.

Note: Here, the break statement may resolve the issue but one must remember that it cannot be used directly since it only exits from the innermost loop.

      for ( ... )
           for ( ... ) {
               ...
               if (condition_causing_disaster)
                   goto error;
           }
       ...
   error: error_statement

In the above lines of code, the former suggested organization is compatible if the error-handling code is non-trivial, and if the occurrence of errors is bound to be in several places.

Label Statement in C

A Label in C is used with goto and switch statements. A label is followed by a colon and what makes it special is that it has the same form as a variable name. Also,it can be adjoined with any statement in the same function as the goto. The label differs from the other statements of its kind is the scope. The scope of a label is the entire function.

Application

Example 1:   

   for (i = 0; i < n; i++)
           for (j = 0; j < m; j++)
               if (x[i] == y[j])


                   goto found;  //no common element found
       …


   found:
       /* found one common element : x [i] == y [j] */
       ...

Code explanation:

The above code is an attempt to solve the problem of determining whether two arrays x and y have an element in common. But this statement can be written in a more elegant way or we can say the easy approach. The above code uses the goto statement to solve the given condition.

But the code consisting of a goto statement can always be written without using this statement. It may cause the programmer trouble with repeated tests (testing conditions) or an extra variable.

Example 2:

  found = 0;
   for (i = 0; i < n && !found; i++)
       for (j = 0; j < m && !found; j++)


           if (x [i] == y [j])
               found = 1;
   if (found)
       // found one common element : x [i] == y [j]
       ...
   else
       // didn't find any common element 
       ...

It is commonly observed that the code that relies on goto statements is generally harder to understand. Not only is it harder to decode but also to maintain as compared to code without gotos.

Conclusion

The goto and label statements do come with its own advantages and the programmer tasks by reducing the number of lines of code (eg: reducing the number of testing conditions), but it is also true that they make the program quite hard to understand and decode.



ADVERTISEMENT
ADVERTISEMENT