argc and argv

Learn command-line arguments with argc and argv.

argc and argv

In C, command-line arguments reach the main function through two parameters: argc and argv. argc is an integer holding the argument count; argv is an array of string pointers, one per argument.

The first entry argv[0] is always the program name. Real user arguments start at argv[1]. For example, running ./prog apple pear gives argc 3; argv[1] is "apple", argv[2] is "pear". This lets you change the program's behavior at run time.

The main signature

To receive arguments you write main as int main(int argc, char *argv[]). Here argv is an array of char *; each element points to a string.

Parameter names are free; int main(int ac, char **av) also works. What matters is the type order: first int, then a char * array. Writing int main(void) means the program cannot access arguments. Most toolchains still place them in memory; the standard way is to declare the signature explicitly.

Exercise Print the argc value

Write the signature int main(int argc, char *argv[]). Print argc with printf using the format "argc=%d\n". End with return 0.

Show example solution

#include <stdio.h>

int main(int argc, char *argv[]) {
    printf("argc=%d\n", argc);
    return 0;
}

Test yourself

What does argc hold?
- The argument count
- The address of the first argument
- The program return code
- The string length
Show answer

The argument count — argc holds the number of command-line arguments.

Print the argc value

printf("argc=%d
", ____);

Show answer

printf("argc=%d
", argc);

Match the argc/argv parts

argc

Argument count
argv[0]

Program name
argv[1]

First user argument
char *argv[]

String pointer array

Next lesson: Argument processing

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