Wsign-conversion.c

// Tested with gcc 10.2.0 and -std=c99
// Author: github.com/Costava

int main(void) {
    // gcc will NOT warn about this line from -Wall or -Wextra
    // -Wsign-conversion is needed:
    /// warning: unsigned conversion from ‘int’ to ‘unsigned int’ changes
    //           value from ‘-1’ to ‘4294967295’ [-Wsign-conversion]
    const unsigned int foo0 = -1;

    // Even with -Wall, -Wextra, and -Wsign-conversion,
    // this line does not cause a warning
    const unsigned int foo1 = -1u;
    // Info on integer constant suffixes:
    // https://en.cppreference.com/w/c/language/integer_constant

    const unsigned int bar = foo0 + foo1 + 5;

    // Even though bar is known at compile time to be in range of int type,
    // -Wsign-conversion still warns for this line:
    // warning: conversion to ‘int’ from ‘unsigned int’ may change the sign of
    //          the result [-Wsign-conversion]
    return bar;// Returns 3
}