为什么输入2的时候输出的是10

Question

#include<stdio.h>
int main()
{
int a=0,b=1,i,n,sum=0;
scanf("%d",&n);
if(n==1)
printf("%d",a);
else if(n==2)
printf("%d",a+1);
else
{
for(i=3;i<=n;i++)
{
sum=a+b;
a=b;
b=sum;
}
}
printf("%d",sum);

}

Answer 1

不是10，是1和0
最后printf(sum)放错位置了

#include<stdio.h>
int main() {
    int a = 0, b = 1, i, n, sum = 0;
    scanf("%d", &n);
    if(n == 1)
        printf("%d", a);
    else if(n == 2)
        printf("%d", a + 1);
    else {
        for(i = 3; i <= n; i++) {
            sum = a + b;
            a = b;
            b = sum;
        }
        printf("%d", sum);
    }
}