Functions in c

  • A function is a self-contained block or a sub-program of one or more statements that performs a special task when called.
  • The programs written in C language highly depends upon functions. The C program is nothing but a combination of one or more functions.
  • Every C program starts with user-defined function main(). Each time when a new program is written, main() function must be defined. The main() calls another function to share the work.
  • The main program to each function can supply data. A specific operation is performed on the data and value is returned to the calling function.
  • Any C program contains at least one function.
  • If a program contains only one function, it must be main( ).
  • If a C program execution always begins with main( ), so it will necessory to define at least one function.
  • There is no limit on the number of functions that might be present in a C program.
  • Each function in a program is called in the sequence specified by the function calls in main( ).
  • After each function has done its thing, control returns to main( ).When main( ) runs out of function calls, the program ends.
  • A function get call when the function name is followed by a semicolan( ; )
  • Any function can be called from any other function. Even main( ) can be called from other functions.
  • A function can be called any number of times.
  • A function can call itself. Such a process is called ‘recursion’.


    data type function (argument 1, argument 2)
          //functions body;


    #include <stdio.h>
    int main()
        int x = 3;
        int x = 6;
        z = add`(x,y);    // Function Call
        add(a,b);       // Function Definition



Why use functions ?

  • If we want to perform a task repetitively, then it is not obligatory to rewrite the particular block of the program again and again. Shift the particular block of statements in an user-defined function. The function defined can be called any number of times depending upon the requirement to perform the task.
  • Using functions, large size programs can be reduced to smaller ones. It is easy to debug and find out the errors in it. It also increases readability.

How Function Works?

  • Once a function is defined and called, it takes some data from the calling function and returns a value to the called function.
  • The detail of inner working of a function is unknown to the rest of the program. Whenever a function is called, control passes to the called function and working of calling function is paused.
  • When the execution of called function is completed, control returns back to the calling function and executes the next statement.
  • The values of actual arguments passed by the calling function are received by the formal arguments of the called function.
  • The number of actual and formal arguments should be the same. Extra arguments are discarded if they are defined.
  • If the formal arguments are more than the actual arguments, then the extra arguments appear as garbage. Any mismatch in the data type will produce the unexpected result.
  • The function operates on formal arguments and sends back the result to calling function. The return statement performs this task.