Command Line Argument in C Programming

In C programming often a situation may come where we want to pass the information into a program during the execution of the program. These values are called Command Line Arguments(CLA).

The “main()” function handles the command line argument.

Syntax:

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

}

Here, argc refers to the number of arguments passed and argv[] is a pointer array that points to each argument.

Note:

argc – argument count in command line argv[0]– holds the name of the program
argv[1]– holds the first command line argument,
argv[2]– holds the second command line argument and and so on.
If no argument is supplied, argc will be 1

          

Program1: Write a program to take one value from user during execution as a Command Line Argument in C Language

#include   	
int  main(int argc, char *argv[] ) 
{  
     printf("\nNo of command line arguments are %d",argc);
     printf("\nProgram name is: %s  ", argv[0]);  
     printf("\nCommand line argument is: %s", argv[1]);  
    return 0;
}

Note: Suppose the above program name is “CLA”.

Run this program as follows in Linux:

./CLA hello

Here hello is a command line argument.

Run this program as follows in Windows from the command line:

program.exe  hello

 Here hello is a command line argument.

Program 2: Write A Program to Add two numbers using Command Line Argument in C Programming

#include 
#include 
int main(int argc, char * argv[]) {
    int sum;
    if (argc != 3) {
        printf("Please enter two integer numbers to add");
        exit(1);
    }
    sum = atoi(argv[1]) + atoi(argv[2]);
    printf("Sum is %d", sum);
    return 0;
}

to convert string to integer atoi() method is used. Similar to convert string to float atof() is used

Compiling and running above program

gcc add.c ./a.out 5 6

Program3: Write a program in a C to take 4 names input from command line argument and print it.

#include 
#include 
 
int main(int argc, char *argv[])   //  command line arguments
{
if(argc!=5) 
{
   printf("Pass four arguments from command line");
   exit(1);
}
 
   printf("\n Program name  : %s \n", argv[0]);
   printf("\n 1st arg  : %s ", argv[1]);
   printf("\n 2nd arg  : %s ", argv[2]);
   printf("\n 3rd arg  : %s ", argv[3]);
   printf("\n 4th arg  : %s ", argv[4]);
    
return 0;
}

Note: Suppose above program name is “names.c”.

gcc names.c ./names RAM MOHAN SOHAN RAMESH

Program4: Find the radius of the circle and take the area input from the command line argument

#include
#include
int main(int argc, char * argv[]) {
    float area, radius;
    if (argc != 2) {
        printf("Please enter circle radius");
        exit(1);
    }
    radius = atof(argv[1]);
    area = 3.14 * radius * radius;
    printf("Area of circle = %0.2f\n", area);
    return 0;
}

gcc circle.c ./circle 5

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