Comparison Between Signed and Unsigned

Description

The program compares signed and unsigned integers, which can lead to unexpected results due to type conversion.

Common Causes

• Comparing signed and unsigned variables directly
• Using size_t (unsigned) with int (signed) in loops
• Mixing signed and unsigned in arithmetic operations

Example of Error

Error Code

int main() {
    int signed_var = -1;
    unsigned int unsigned_var = 1;
    
    if (signed_var < unsigned_var) {
        printf("signed_var is less\n");
    } else {
        printf("unsigned_var is less\n");  // This will execute!
    }
    
    return 0;
}

Solution

Cast variables to the same type before comparing them.

Corrected Code

int main() {
    int signed_var = -1;
    unsigned int unsigned_var = 1;
    
    if ((long long)signed_var < (long long)unsigned_var) {
        printf("signed_var is less\n");  // This will execute
    } else {
        printf("unsigned_var is less\n");
    }
    
    return 0;
}

Additional Tips

• Be careful when comparing signed and unsigned values
• Cast to a common type before comparison
• Be aware that negative signed values become large positive values when converted to unsigned
• Use consistent types for related variables