求两个数相加的c语言程序

我晕~
#include<stdio.h>
void sum(int a,int b)
{
printf("%d\n",a+b);
}
void main()
{
int a,b;
scanf("%d%d",&a,&b);
sum(a,b);
}

#include <stdio.h>

int sum(int a, int b);

int main(void)
{
int a = 123, b = 456;

printf("a + b = %d", sum(a, b));
}

int sum(int a, int b)
{
return a + b;
}

public int sum(int a, int b) {
int count = 0;
count = a + b;
return count;
}