Introduction to Programming in C

📘 Command Line Arguments in C

Command line arguments allow users to pass values to a C program during its execution from the terminal. This enables flexible and dynamic behavior based on input, making programs more useful and interactive.

🔹 Syntax

int main(int argc, char *argv[]) {
    // Your code here
}

• argc: Argument Count – Number of command-line arguments passed
• argv: Argument Vector – Array of strings (character pointers) representing the arguments

📂 Basic Example

#include <stdio.h>

int main(int argc, char *argv[]) {
    printf("Number of arguments: %d\n", argc);

    for (int i = 0; i < argc; i++) {
        printf("Argument %d: %s\n", i, argv[i]);
    }

    return 0;
}

If compiled as ./program hello world, output will be:

Number of arguments: 3
Argument 0: ./program
Argument 1: hello
Argument 2: world

📚 UdaanPath Example: Dynamic Welcome

#include <stdio.h>

int main(int argc, char *argv[]) {
    if (argc < 2) {
        printf("Usage: %s <username>\n", argv[0]);
        return 1;
    }

    printf("👋 Welcome to UdaanPath, %s!\n", argv[1]);
    return 0;
}

This program greets the user with their name passed as a command-line argument. Example: ./welcome Kuldeep

🧠 Notes

• Arguments are always passed as strings (char *).
• You can use atoi(), atof() to convert them into numbers.
• Use argv[0] to get the program name.

🔁 Argument Conversion

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

int main(int argc, char *argv[]) {
    if (argc < 3) {
        printf("Usage: %s num1 num2\n", argv[0]);
        return 1;
    }

    int a = atoi(argv[1]);
    int b = atoi(argv[2]);
    printf("Sum: %d\n", a + b);
    return 0;
}

📝 Practice Exercises

1. Create a program to calculate factorial of a number using command-line input.
2. Write a program to convert Celsius to Fahrenheit using arguments.
3. Create a program that accepts a filename via command line and writes “Hello from UdaanPath” into it.

✅ Summary

• Use argc and argv[] to receive command-line arguments.
• All command-line arguments are received as strings.
• Convert strings to integers/floats when required using utility functions.

🚀 Coming Next

In the next and final chapter, we’ll learn about Error Handling and errno — how to gracefully handle errors and check system-level error codes.