怎么改错，有人能讲解下吗

Question

#include<stdio.h>
int main()
{
int a, b;
scanf("%d%d",&a,&b);
printf("%d\n",sum(a+b));
int sum(int a,b)
{
sum=a+b;
return sum;
}
return 0;
}

Answer 1

#include<stdio.h>
int sum(int a,int b);
int main()
{
    int a, b;
    scanf("%d%d",&a,&b);
    printf("%d\n",sum(a,b));
    return 0;
}
int sum(int a,int b)
{
    int sum;
    sum=a+b;
    return sum;
}

//你问题是子函数和主函数没有分开，调用子函数参数错误，不声明子函数，子函数中变量名sum和函数名sum不同