c++ - 错误 : Expression must be a modifiable lvalue using strings

Question

我正在尝试创建一个函数来计算特定字符在字符串中的使用次数。给我错误的部分是:

s[i] = tolower(s[i]);

代码:

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

unsigned howMany(char c, const string & s);
string changeCase(const string & s);

int main() {
    char z;
    string name;
    cout << "Enter char and string: ";
    cin >> z;
    getline(cin, name, '\n');
    cout << howMany(z, name) << endl;
    cout << changeCase(name) << endl;
}

unsigned howMany(char c, const string & s) {
    unsigned count = 0;
    for (unsigned i = 0; i < s.size(); i++)
    {
        if (c == s[i]) { count++; }

            if (isupper(s[i])){ s[i] = tolower(s[i]);
            count++; 
        }
    }
    return count;
}

Answer 1

您将 s 声明为 const。你无法改变它。