VS运行正常但是不能AC……

#include<iostream>
#include<string>
#include<cmath>
#include<cstdio>
using namespace std;

string fstwrd; char c_;
int sec, trd;
int trans(string a)//把字符串变成数字
{
	int res;
	for (int i = 0; i < a.size(); i++)
	{
		res = pow(10, i) * (a[i] - '0');
	}
	return res;
}
int weishu(int a) {//计算位数
	a = fabs(a); int x = 0;
	if (a == 0) return 1;
	while (a) {
		a /= 10;
		x++;
	}
	return x;
}
int main()
{
	int n; cin >> n;int len;
	for (int i = 0; i < n; i++) {
		cin >> fstwrd;
		switch (fstwrd[0]) {
		case'a':c_ = fstwrd[0]; cin >> sec >> trd;
			 len = weishu(sec) + weishu(trd) + weishu(sec + trd);
			printf("%d+%d=%d\n%d", sec, trd, sec + trd, len + 2); break;
		case'b':c_ = fstwrd[0]; cin >> sec >> trd;
			 len = weishu(sec) + weishu(trd) + weishu(sec - trd);
			printf("%d-%d=%d\n%d", sec, trd, sec - trd, len + 2); break;
		case'c':c_ = fstwrd[0]; cin >> sec >> trd;
			 len = weishu(sec) + weishu(trd) + weishu(sec * trd);
			printf("%d*%d=%d\n%d", sec, trd, sec * trd, len + 2); break;
		default:
			cin >> trd; sec = trans(fstwrd);
			switch(c_) {
		case'a': len = weishu(sec) + weishu(trd) + weishu(sec + trd);
			printf("%d+%d=%d\n%d", sec, trd, sec + trd, len + 2); break;
		case'b': len = weishu(sec) + weishu(trd) + weishu(sec - trd);
			printf("%d-%d=%d\n%d", sec, trd, sec - trd, len + 2); break;
		case'c': len = weishu(sec) + weishu(trd) + weishu(sec * trd);
			printf("%d*%d=%d\n%d", sec, trd, sec * trd, len + 2); break;
		default:break;
			}
			
			break;
			}
			printf("\n"); 
	}
	return 0; 
}