In a function two return statements should never occur.

No, In a function two return statements can occur but not successively.

Example:

#include <stdio.h>
int mul(int, int); /* Function prototype */

int main()
{
    int a = 0, b = 3, c;
    c = mul(a, b);
    printf("c = %d\n", c);
    return 0;
}

/* Two return statements in the mul() function */
int mul(int a, int b)
{
   if(a == 0 || b == 0)
   {
        return 0;
   }
   else
   {
        return (a * b);
   }
}

Output:
c = 0