C Command Line Arguments

We can give values to a program when we start it from the terminal. These are called command line arguments. To receive them, main() takes two parameters.

int main(int argc, char *argv[])

• argc is the number of arguments, including the program name.
• argv is an array of strings. argv[0] is the program name, argv[1] is the first argument, and so on.

Example: add two numbers

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

int main(int argc, char *argv[]) {
    if (argc != 3) {
        printf("Usage: sum number1 number2\n");
        return 1;
    }

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

Compile it, and then run it with two numbers.

gcc sum.c -o sum
./sum 10 20

Output:

Print all arguments

#include <stdio.h>

int main(int argc, char *argv[]) {
    printf("Total arguments: %d\n", argc);
    for (int i = 1; i < argc; i++) {
        printf("Argument %d: %s\n", i, argv[i]);
    }
    return 0;
}

./show red green blue

Output:

You have finished the C tutorial. Now practice with the C exercises, and then try small programs of your own.

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