大佬帮忙看看吧，输入输出一模一样但是全WA

#include <bits/stdc++.h>
using namespace std;
const int N=55;
char str[20],ans[20];
int n;
char op;
int main(){
    scanf("%d",&n);
    getchar();
    for(int i=1;i<=n;i++){
        fgets(str,sizeof str,stdin);
            if(str[0]=='a'||str[0]=='b'||str[0]=='c'){
                op=str[0];
               str[0]=' ';

            }
          int a=0,b=0,c=0;
          sscanf(str,"%d %d",&a,&b);
          if(op=='a'){
             sprintf(ans,"%d+%d=%d",a,b,c=a+b);

          }
          else if(op=='b'){
               sprintf(ans,"%d-%d=%d",a,b,c=a-b);
          }
          else{
               sprintf(ans,"%d*%d=%d",a,b,c=a*b);
          }
           printf("%s\n%d\n",ans,strlen(ans));
        }
        return 0;
    }