检测字符串中的负整数

Question

Say I take in a string of input and I wanted to check if the user entered a negative number.

bool isNegative(string input[]) {
    int i = 0;
    if (input[i] == "-") {
        return true;
    } else {
        return false;
    }
}

I tried a boolean function to check if the first character is a - sign, representing negative numbers eg -5, -25.

However, my Netbeans gave me this error: main.cpp:39:25: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]

anyone knows what this means?

Answer 1

There are two problems with your code:

• You declare i that never changes. This is the same as doing input[0]
• You compare a character to a string. Instead of "0" (double quotes) you need '0' (single quotes).

Fixing these two problems will fix your code.

Note: You can write this function in a single line:

bool isNegative(string input) {
    return input[0] == '-';
}

Answer 2

您需要使用单引号表示单个字符，而不是使用双引号表示字符串。

if (input[i] == '-')