Command line arguments example in C

Prerequisite: Command_line_argument.

The problem is to find the largest integers among three using command line argument.


  • Command-line arguments are given after the name of the program in command-line shell of Operating Systems. To pass command line arguments, we typically define main() with two arguments : first argument is the number of command line arguments and second is list of command-line arguments.
    int main(int argc, char *argv[]) { /* ... */ }
  • atoi – Used to convert string number to integers

  • Examples:

    Input  : filename 8 9 45
    Output : 45 is largest
    Input  : filename 8 9 9
    Output : Two equal number entered
    Input  : filename 8 -9 9
    Output : negative number entered

    During execution of program, we pass three integers along with filename of the program and then we will find the largest numbers among three.
    Approach :

    1. The program “return 1” if any of the two conditions satisfy:
      • If any two numbers are same, print the statement “two equal numbers entered”.
      • If any number is negative, print “negative number entered”.
    2. Else “return 0” if three different integers are entered.

    For better understanding run this code on your linux machine.





    // C program for finding the largest integer
    // among three numbers using command line arguments
    // Taking argument as command line
    int main(int argc, char *argv[]) 
        int a, b, c;
        // Checking if number of argument is
        // equal to 4 or not.
        if (argc < 4 || argc > 5) 
            printf("enter 4 arguments only eg.\"filename arg1 arg2 arg3!!\"");
            return 0;
        // Converting string type to integer type
        // using function "atoi( argument)" 
        a = atoi(argv[1]); 
        b = atoi(argv[2]);
        c = atoi(argv[3]);
        // Checking if all the numbers are positive of not
        if (a < 0 || b < 0 || c < 0) 
            printf("enter only positive values in arguments !!");
            return 1;
        // Checking if all the numbers are different or not
        if (!(a != b && b != c && a != c)) 
            printf("please enter three different value ");
            return 1;
            // Checking condition for "a" to be largest
            if (a > b && a > c)             
                printf("%d is largest", a);
            // Checking condition for "b" to be largest    
            else if (b > c && b > a) 
                printf ("%d is largest", b);
            // Checking condition for "c" to be largest..
            else if (c > a && c > b) 
                printf("%d is largest ",c);
        return 0;



    Output :

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