How Does C Handle Comparisons Between Signed and Unsigned Integers?

Comparison of Signed and Unsigned Types in C

In C , when comparing a signed integer with an unsigned integer, the signed integer is promoted to an unsigned integer. This means that the negative sign is ignored and the integer is treated as a large positive value.

Consider the following C program:

#include <iostream>
#include <vector>

int main() {
    std::vector<int> a;
    std::cout << "Vector size: " << a.size() << std::endl;

    int b = -1;
    if (b < a.size())
        std::cout << "Less";
    else
        std::cout << "Greater";
}

In this program, the size of the vector a is an unsigned integer. However, when comparing it to the signed integer b, b is promoted to an unsigned integer. This means that the negative sign is ignored and b is treated as a large positive value. Therefore, the comparison b < a.size() will always be false, and the program will print "Greater."

To see this behavior more clearly, consider the following code sample:

#include <iostream>

int main()
{
    unsigned int a = 0;
    int b = -1;
    std::cout << std::boolalpha;
    std::cout << (b < a) << "\n";
}

This program will output false, even though b is obviously less than a. This is because b is promoted to an unsigned integer, and the negative sign is ignored.

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