按照书上的思路的

#include<bits/stdc++.h>
using namespace std;
int main(){
    int n,a,b;cin>>n;
    char fu,s[20],ans;cin>>fu;
    for(int i=0;i<n;i++){
        fgets(s,sizeof(s),stdin);
        if(s[0]=='a'||s[0]=='b'||s[0]=='c')
            fu=s[0];s[0]=' ';
        sscanf(s,"%d %d",&a,&b);
        if(fu=='a') sprintf(ans,"%d+%d=%d",a,b,a+b);
        else if(fu=='b') sprintf(ans,"%d-%d=%d",a,b,a-b);
        else sprintf(ans,"%d*%d=%d",a,b,a*b);
        printf("%s/n%d/n",ans,strlen(ans));
    }
    return 0;
}