Thread: Function Question

Hi im just wondering if there is a differnce between

Code:

#include <stdio.h>

int twice(int i);

int main(void)
{
    int input;

    printf("Enter number to be doubled: ");
    scanf("%d", &input);

    printf("%d X 2 = %d\n", input, twice(input));
}

int twice(int i)
{
    return (i * 2);
}

and

Code:

#include <stdio.h>

int twice(int i)
{
    return (i * 2);
}

int main(void)
{
    int input;

    printf("Enter number to be doubled: ");
    scanf("%d", &input);

    printf("%d X 2 = %d\n", input, twice(input));
}

no difference whatsoever, other than one uses a prototype because the function twice() isn't defined until after it is called. Writing it either way is correct.

The main difference is that in second case you dont need to decleare the function but in first case you have to.

This is because program starts compiling from top to bottom.so in first case when it found function declearation then it(compiler) makes entry for it in its funtion table.and when it is called then it will move up to defination part that is at last in your example.

while in second case you have make function defination before main() which will save your work that is function defination eliminates the need of its delclaration.

so doing both is good as well but most of people use the first way to make there program to give a clearer understanding.