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return Statement (C)

The return statement terminates the execution of a function and returns control to the calling function. Execution resumes in the calling function at the point immediately following the call. A return statement can also return a value to the calling function. See Return Type for more information.


return expression opt ;

The value of expression, if present, is returned to the calling function. If expression is omitted, the return value of the function is undefined. The expression, if present, is evaluated and then converted to the type returned by the function. If the function was declared with return type void, a return statement containing an expression generates a warning and the expression is not evaluated.

If no return statement appears in a function definition, control automatically returns to the calling function after the last statement of the called function is executed. In this case, the return value of the called function is undefined. If a return value is not required, declare the function to have void return type; otherwise, the default return type is int.

Many programmers use parentheses to enclose the expression argument of the return statement. However, C does not require the parentheses.

This example demonstrates the return statement:

#include <limits.h>
#include <stdio.h>

void draw( int i, long long ll );
long long sq( int s );

int main()
    long long y;
    int x = INT_MAX;

    y = sq( x );
    draw( x, y );
    return x;

long long sq( int s )
    // Note that parentheses around the return expression 
    // are allowed but not required here.
    return( s * (long long)s );

void draw( int i, long long ll )
    printf( "i = %d, ll = %lld\n", i, ll );

In this example, the main function calls two functions: sq and draw. The sq function returns the value of x * x to main, where the return value is assigned to y. The parentheses around the return expression in sq are evaluated as part of the expression, and are not required by the return statement. Since the return expression is evaluated before it is converted to the return type, sq forces the expression type to be the return type with a cast to prevent a possible integer overflow, which could lead to unexpected results. The draw function is declared as a void function. It prints the values of its parameters and then the empty return statement ends the function and does not return a value. An attempt to assign the return value of draw would cause a diagnostic message to be issued. The main function then returns the value of x to the operating system.

The output of the example looks like this:

i = 2147483647, ll = 4611686014132420609
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