How to Write a Command Line Program in C?

Last Updated : 07 Feb, 2024

In C, we can provide arguments to a program while running it from the command line interface. These arguments are called command-line arguments. In this article, we will learn how to write a command line program in C.

How to Write a Command Line Program in C?

Command line arguments are passed to the main() function. For that purpose, the main function should have the following signature:

int main( int argc , char *argv[] ){
     // Write your code
}

Here, argc is the number of arguments, and argv[] is the argument in the form of an array of strings.

Note: The argv[0] always contains the source file name.

C Program to Pass Command Line Arguments

C

// Program to demonstrate Command line arguments in C 
#include <stdio.h> 
#include <stdlib.h> 
  
int main(int argc, char* argv[]) 
{ 
    // code to calculate the sum of n numbers passed to CLA 
    int i, sum = 0; 
  
    // iterating the loop till the the number of 
    // command-line arguments passed to the program 
    // starting from index 1 
    for (i = 1; i < argc; i++) { 
        sum = sum + atoi(argv[i]); 
    } 
    printf("Sum of %d numbers is : %d\n", argc - 1, sum); 
    
    return 0; 
}

Command Line Instruction

// assume that the file name is solution
./solution 10 20 30 40 50

Output

SUM of 5 numbers is: 150

Note: The command line arguments are separated by space so if you want to pass a space-separated string as a command line argument, then enclose them inside the “”.

To know more, refer to the article – Command Line Arguments in C

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