时隔一个月！！！成功！！！ohhhhhh

找到问题了，在cmp函数里如果a[i]<b[i]会跳过，不会判断小于
AC题解

#include <iostream>
#include <cstring>
using namespace std;
bool cmpp(char a[], char b[], int len){//判断是否相等
	for(int i = 0; i < len; i++){
		if(a[i] != b[i]) return 0;
	}return 1;
}
bool cmp(char a[], char b[], int len){//判断大小
	for(int i = 0; i < len; i++){
		//cout << int(a[i]) << ' ' << int(b[i]) << endl;
		if(a[i] > b[i]){
			//cout << a[i] << ' ' << b[i];
			return 1;
		}else if(a[i] < b[i])return 0;//之前就这里错了！！！
	}
}
int main(){
    string a, b;
    cin >> a >> b;
    char a1[1005] = {0}, b1[1005] = {0};
    bool flag1 = 0, flag2 = 0;
    int ct1 = 0, ct2 = 0;
    for(int i = 0; i < a.length(); i++){
    	if(a[i] == '.') break; //去除小数点
    	if(!flag1 && a[i] != '0') flag1 = 1;//去除前导0
    	if(flag1) a1[ct1++] = a[i];
	}for(int i = 0; i < b.length(); i++){
		if(b[i] == '.') break;
    	if(!flag2 && b[i] != '0') flag2 = 1;
    	if(flag2) b1[ct2++] = b[i];
	}
	//cout << a1 << endl << b1 << endl;
    if(cmpp(a1, b1, max(strlen(a1), strlen(b1)))) cout << '=';
    else if(strlen(a1) > strlen(b1) || strlen(a1) == strlen(b1) && cmp(a1, b1, strlen(a1))) cout << '>';
    else cout << '<';
}