arguments in C

If your main.c looks like this:

int main() {
    // Here is the code.
}

cannot accept the argument from the command line, because that signature (int main()) does not expect to receive arguments from the operating system.

---

should look like this:

int main(int argc, char *argv[]) { ... }

Read the second word you type in the terminal (argv[1])

---

You must use the variable argv[1]

Also, you must put in an initial check to make sure the user actually supplied the argument

---

argv[0] is always the name of the program (or path) that is running

---

• argv[0] is for the program
• argc (parameter the counter) is always at least 1 (because argv[0] always exists)
• argv[1] onwards are for user data

---

For example, if you want to enter an “int” as arguments

• Capture the text string using argv[1]
• Convert that string to an integer using a special C function

You need to use the atoi (ASCII to Integer) function from the from the <stdib.h> library

Capture the argument “3” from the command line

const char *var1 = argv[1];

CONVERSION: Use atoi() to convert the string (“3”) to an integer (3)

int var2 = atoi(var1);

---

example:

code of “a.c”:

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

int main(int argc, char *argv[]) { 
const char *var1 = argv[1];
int var2 = atoi(var1);
printf("%d\n", var2);
 }

compiles a.c and creates the executable a (with gcc)

 gcc a.c -o a

execute a with argument 123

./a 123

You should see 123 in the console/terminal.