Error Messages

GLaDOS provides detailed error messages to help you debug your programs. This guide explains common errors and how to fix them.

Compile-Time Errors

All errors below are caught during compilation (before your program runs).

Type Errors

Type Mismatch in Assignment

int x = true;

Error:

Type error at line 1: expected int but got bool

Fix: Use matching types:

int x = 42;
bool flag = true;

Type Mismatch in Return

int getValue() {
    return true;  // Returning bool from int function
}

Error:

Return type mismatch at line 2: expected int but got bool

Fix:

int getValue() {
    return 42;
}

Type Mismatch in Operations

int x = 5;
bool y = true;
int z = x + y;

Error:

Type error in arithmetic at line 3: expected int but got bool

Fix: Don't mix types in arithmetic:

int x = 5;
int y = 10;
int z = x + y;  // Both operands are int

Type Mismatch in Conditionals

int x = 5;
while (x) {  // int where bool expected
    x = x - 1;
}

Error:

Type error at line 2: expected bool but got int

Fix: Use a comparison:

while (x > 0) {
    x = x - 1;
}

Function Errors

Undefined Function

int main() {
    return multiply(5, 3);  // multiply not defined
}

Error:

Undefined function 'multiply' at line 2

Fix: Define the function before calling it:

int multiply(int a, int b) {
    return a * b;
}

int main() {
    return multiply(5, 3);
}

Wrong Argument Count

int add(int a, int b) {
    return a + b;
}

int main() {
    return add(5);  // Missing one argument
}

Error:

Function 'add' expects 2 arguments but got 1 at line 6

Fix: Provide all required arguments:

return add(5, 3);

Wrong Argument Types

int add(int a, int b) {
    return a + b;
}

int main() {
    bool x = true;
    return add(x, 5);  // bool passed where int expected
}

Error:

Type mismatch in function argument at line 7: expected int but got bool

Fix: Use correct types:

int x = 10;
return add(x, 5);

Variable Errors

Undefined Variable

int main() {
    return x;  // x not defined
}

Error:

Undefined variable 'x' at line 2

Fix: Declare the variable first:

int main() {
    int x = 42;
    return x;
}

Uninitialized Variable

int main() {
    int x;
    return x;  // x declared but not initialized
}

Error:

Variable 'x' used before initialization at line 3

Fix: Initialize before use:

int main() {
    int x = 42;
    return x;
}

Or assign a value:

int main() {
    int x;
    x = 42;
    return x;
}

Variable Used Before Declaration

int main() {
    int y = x + 1;  // x used before declaration
    int x = 5;
    return y;
}

Error:

Undefined variable 'x' at line 2

Fix: Declare variables before using them:

int main() {
    int x = 5;
    int y = x + 1;
    return y;
}

Return Statement Errors

Missing Return Statement

int getValue(int x) {
    if (x > 0) {
        return 1;
    }
    // Missing return for x <= 0
}

Error:

Function 'getValue' must return a value on all code paths

Fix: Add an else branch with return:

int getValue(int x) {
    if (x > 0) {
        return 1;
    } else {
        return 0;
    }
}

Or a return after the if:

int getValue(int x) {
    if (x > 0) {
        return 1;
    }
    return 0;
}

Empty Function Body

int main() {
}

Error:

Function 'main' must return a value on all code paths

Fix: Add a return statement:

int main() {
    return 0;
}

Division Errors

Division by Zero (Literal)

int main() {
    int x = 10 / 0;
    return x;
}

Error:

Division by zero at line 2

Fix: Don't divide by literal zero:

int main() {
    int x = 10 / 2;
    return x;
}

Note: Division by zero with variables is only caught at runtime:

int divide(int a, int b) {
    return a / b;  // OK at compile time
}

int main() {
    return divide(10, 0);  // Runtime error!
}

Parse Errors

Syntax Errors

Missing Semicolon

int main() {
    int x = 5
    int y = 10;
    return x + y;
}

Error:

Parse error: unexpected token at line 3

Fix: Add semicolons (though GLaDOS is lenient):

int x = 5;
int y = 10;

Mismatched Braces

int main() {
    int x = 5;
    return x;
// Missing closing brace

Error:

Parse error: unexpected end of input

Fix: Close all braces:

int main() {
    int x = 5;
    return x;
}

Invalid Token

int main() {
    int x = 5 @ 3;  // @ is not a valid operator
    return x;
}

Error:

Parse error: unexpected character '@' at line 2

Fix: Use valid operators:

int x = 5 + 3;

Runtime Errors

These errors occur during program execution:

Division by Zero (Runtime)

int divide(int numerator, int denominator) {
    return numerator / denominator;
}

int main() {
    int result = divide(10, 0);
    return result;
}

Error:

Runtime error: Division by zero

Fix: Check for zero before dividing:

int divide(int numerator, int denominator) {
    if (denominator == 0) {
        return 0;  // Or handle error appropriately
    }
    return numerator / denominator;
}

Stack Overflow (Deep Recursion)

int infinite(int x) {
    return infinite(x + 1);  // Never stops!
}

This may cause a stack overflow. Always ensure recursion has a base case.

Error Message Format

GLaDOS error messages follow this format:

<Error Type>: <Description> at <Source Position>

Where:

• Error Type: Type error, Parse error, Runtime error, etc.
• Description: What went wrong
• Source Position: File location (line and column)

Example:

Type error in arithmetic at input:5:12: expected int but got bool

Tips for Debugging

1. Read the error message carefully - it tells you exactly what's wrong
2. Check the line number - the error is usually on or near that line
3. Look at variable types - most errors are type mismatches
4. Verify all code paths return - use else branches
5. Initialize variables before using them
6. Match function signatures - check parameter counts and types
7. Test incrementally - compile often to catch errors early

Exit Codes

GLaDOS uses standard Unix exit codes:

• 0: Success, no errors
• 84: Compilation or runtime error (EPITECH standard)