Parsing numeric arguments - Mini Project: Build & Apply

Parsing numeric arguments

📖 Scenario: You are writing a simple C program that takes a number as a command-line argument and processes it.This is common when programs need input values from the user when starting.

🎯 Goal: Build a C program that reads a numeric argument from the command line, converts it to an integer, and prints it.

📋 What You'll Learn

Create a variable to hold the argument string

Create a variable to hold the converted integer

Use argc and argv to access command-line arguments

Use atoi to convert the string argument to an integer

Print the integer value using printf

💡 Why This Matters

🌍 Real World

Many command-line tools and programs accept numbers as arguments to control their behavior, like setting a timeout or choosing a mode.

💼 Career

Understanding how to parse and use command-line arguments is essential for software developers working on utilities, scripts, or system programs.

1

Set up main function and argument variables

Write the main function header with parameters int argc and char *argv[]. Inside main, declare a variable char *arg and set it to argv[1] to hold the first command-line argument.

C

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

Need a hint?

Remember, argv[0] is the program name, so the first argument is argv[1].

2

Declare an integer variable for the converted number

Declare an integer variable called num to store the converted number from the argument.

C

int main(int argc, char *argv[]) {
    char *arg = argv[1];
    // Your code here
}

Need a hint?

Just declare the variable num as an int.

3

Convert the argument string to an integer

Use the atoi function to convert arg to an integer and store it in num. Write the line num = atoi(arg);.

C

int main(int argc, char *argv[]) {
    char *arg = argv[1];
    int num;
    // Your code here
}

Need a hint?

Use atoi from stdlib.h to convert the string to an integer.

4

Print the converted integer

Use printf to print the integer num with the message: "The number is: %d\n". Write printf("The number is: %d\n", num);.

C

int main(int argc, char *argv[]) {
    char *arg = argv[1];
    int num;
    num = atoi(arg);
    // Your code here
}

Need a hint?

Use printf with %d to print the integer value.