Why error handling is needed in C - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Why do programs need error handling?

Which of the following best explains why error handling is important in C programs?

A To reduce the size of the program's source code.

B To make the program run faster by skipping checks.

C To ensure the program can detect and respond to unexpected problems during execution.

D To avoid writing comments in the code.

💡 Hint

Think about what happens if something goes wrong while the program runs.

Error handling helps programs detect problems like missing files or invalid input and respond properly instead of crashing.

❓ Predict Output

intermediate

Output when file open fails

What will this C program print if the file data.txt does not exist?

C

#include <stdio.h>
int main() {
    FILE *f = fopen("data.txt", "r");
    if (f == NULL) {
        printf("Error opening file\n");
    } else {
        printf("File opened successfully\n");
        fclose(f);
    }
    return 0;
}

A Error opening file

B File opened successfully

C Compilation error

D No output

💡 Hint

What does fopen return if the file is missing?

If the file does not exist, fopen returns NULL, so the program prints the error message.

❓ Predict Output

advanced

Behavior without error handling

What happens when this C program tries to read from a file that does not exist?

C

#include <stdio.h>
int main() {
    FILE *f = fopen("nofile.txt", "r");
    char buffer[10];
    fread(buffer, sizeof(char), 10, f);
    printf("Read data: %s\n", buffer);
    fclose(f);
    return 0;
}

A Prints empty string

B Undefined behavior, likely a crash or garbage output

C Prints "Read data: nofile.txt"

D Compilation error

💡 Hint

What happens if you use a file pointer that is NULL?

Since fopen returns NULL when the file is missing, using it in fread causes undefined behavior, often a crash.

🧠 Conceptual

advanced

Why check return values in C?

Why is it important to check return values of functions like malloc or fopen in C?

A Because these functions may fail and return NULL, indicating an error that must be handled.

B Because checking return values makes the program run faster.

C Because C requires all functions to have their return values checked by the compiler.

D Because it helps to reduce the size of the executable file.

💡 Hint

Think about what happens if memory allocation or file opening fails.

Functions like malloc and fopen return NULL on failure, so checking their return values helps avoid crashes or undefined behavior.

🔧 Debug

expert

Identify the error handling mistake

What is the main error handling mistake in this C code snippet?

C

#include <stdio.h>
#include <stdlib.h>
int main() {
    int *ptr = malloc(sizeof(int) * 5);
    *ptr = 10;
    printf("Value: %d\n", *ptr);
    free(ptr);
    return 0;
}

A The code frees the pointer before using it.

B The code allocates memory for 5 integers but only uses one.

C The code uses printf incorrectly.

D The code does not check if malloc returned NULL before using the pointer.

💡 Hint

What happens if malloc fails?

If malloc fails, it returns NULL. Using the pointer without checking causes undefined behavior or crashes.