Difference between a compiler error and a runtime error

In the programming world, errors are inevitable in the development process. Developers encounter two common types of errors: compiler and runtime. Understanding the differences between these two types of errors is crucial for effective debugging and troubleshooting.

This Answer aims to explain the differences between compiler errors and runtime errors, providing examples and a comparative table for easy understanding.

Compiler errors

Compiler errors are errors that occur during the compilation phase of software development. The compiler detects these errors and prevents the code from successfully compiling into executable programs.

Examples of compiler errors

Following are the cases where compiler error occurs:

Syntax errors

These errors occur when code violates the language's grammar rules. For instance, forgetting to close parenthesis or adding an extra semicolon can result in syntax errors. 

Consider the following example in Python:

print("Hello, World!"

In this case, the missing closing parenthesis will cause a syntax error.

Type errors

Type errors occur when incompatible data types are used or when a variable is not declared before being used.

Consider the following example in C++:

int num = "Hello";

Here, assigning a string value to an integer variable will result in a type error.

Runtime errors

Runtime errors, or logical errors, occur when the program is executed. Runtime errors can cause the program to crash, produce incorrect results, or generate error messages during execution.

Examples of runtime errors

Following are the cases where a runtime error occurs:

Division by zero

Attempting to divide a number by zero is a common runtime error.

For instance, consider the following example in Java:

#include <iostream>
int main() {
int a = 10;
int b = 0;
int c = a / b;
std::cout << c << std::endl;
return 0;
}

When we try to execute this code, it will produce a runtime error because we are trying to divide a number by zero.

Null pointer exception

This error occurs when a program tries to access or use an object reference that points to null.

Consider the following example in Java:

public class NullPointerExample {
public static void main(String[] args) {
String message = null;
int length = message.length(); // This line throws a Null Pointer Exception
System.out.println("Length: " + length);
}
}

In this case, trying to access the Length property of a null object reference will throw a "NullReferenceException" at runtime.

Compiler errors vs. runtime errors

Compiler errors

Runtime errors

Occur during the compilation phase

Occur during the execution phase

Prevent the code from successfully compiling

Disrupt the normal flow of the program

Result from syntax or semantic mistakes

Caused by unexpected situations or exceptions

Detected by the compiler

Triggered during program execution

Compiler generates error messages

Program may crash or produce incorrect results

Conclusion

Compiler errors occur during compilation and are detected by the compiler. In contrast, runtime errors occur during program execution and are caused by unexpected conditions. Developers need to understand the differences between these two types of errors to write efficient and error-free code.

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