main function and program entry - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this C program?

Consider the following C code. What will it print when run?

C

#include <stdio.h>

int main() {
    printf("Hello, World!\n");
    return 0;
}

A Hello World

B hello, world!

C Hello, World!

D Compilation error

💡 Hint

Look carefully at the exact string inside printf including capitalization and punctuation.

The program prints exactly "Hello, World!" followed by a newline. The printf function outputs the string as is.

❓ Predict Output

intermediate

What is the value of variable x after running this program?

What value does x hold after the program finishes?

C

#include <stdio.h>

int main() {
    int x = 5;
    x = x + 10;
    return 0;
}

A 15

B 5

C 10

D Compilation error

💡 Hint

Remember that x = x + 10; adds 10 to the current value of x.

The variable x starts at 5, then 10 is added, so x becomes 15.

❓ Predict Output

advanced

What is the output of this program with command line arguments?

What will this program print if run with the command ./program 3 7?

C

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[]) {
    if (argc < 3) {
        printf("Not enough arguments\n");
        return 1;
    }
    int a = atoi(argv[1]);
    int b = atoi(argv[2]);
    printf("Sum: %d\n", a + b);
    return 0;
}

A Sum: 10

B Sum: 37

C Not enough arguments

D Runtime error

💡 Hint

Check how argc and argv are used to get command line arguments and convert them to integers.

The program converts the first two arguments "3" and "7" to integers and prints their sum, which is 10.

❓ Predict Output

advanced

What error does this program produce when compiled?

What error will the compiler show for this program?

C

#include <stdio.h>

void main() {
    printf("Hello\n");
}

A Syntax error: missing semicolon

B Warning: return type of 'main' is not 'int'

C No error, program runs fine

D Linker error: undefined reference to 'main'

💡 Hint

Check the return type of the main function in standard C.

The standard C requires main to return int. Using void main() causes a compiler warning.

🧠 Conceptual

expert

How many times is the main function called in a standard C program execution?

In a typical C program, how many times is the main function called during the program's lifetime?

A Depends on the number of threads created

B Multiple times, each time a function calls it

C Zero times, the OS runs the program without calling main

D Exactly once, when the program starts

💡 Hint

Think about the role of main as the program's entry point.

The main function is called exactly once by the operating system when the program starts. It is not called again unless explicitly invoked, which is uncommon and not standard practice.