pass only integer datatype as command line argument in c

Question

I'm new to C programming. I've been practicing use of command line arguments in C. I've written a C code to calculate the area and circumference of a circle. This is my code:

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

float circle(float pi,int r)
{
    float cir;
    cir=(pi*r*r);
    printf("area of the circle is: %f \n",cir);
}
float circumference(float pi,int r)
{
    float circum;
    circum=(2*pi*r);
    printf("the circumference is: %f \n",circum);
}
int main(int argc,char *argv[])
{   int r,r1;
    float pi;
    r=0;
    pi=M_PI;
    if(argc>3 || argc<3)
    {
        printf("error \n");
        exit(0);
    }
    r=atoi(argv[1]);
    r1=atoi(argv[2]);
    circle(pi,r);
    circumference(pi,r1);
}

My results are proper but I want to enhance my code to stop if the argument given is not a number. if not it should be an error. How can I do it? Any leads will be appreciated. Thank you in advance

Thank you for replying. How can I use isdigit for multiple argument @1201ProgramAlarm — ankitha shetty
– ankitha shetty, Commented Jun 14, 2020 at 22:23

Stephan Lechner · Accepted Answer · 2020-06-14 22:23:16Z

1

Unfortunately, atoi returns 0 if parsing fails, though 0 might be a valid input as well.

In C, I see two options to overcome this:

(1) use sscanf and see if exactly one number could be parsed:

if (sscanf(argv[1],"%d",&r) != 1) {
   // some error handling here...
}

(2) check if at least the first character is a digit (yielding a valid number then):

if (!isdigit(argv[1][0]) {
   // some error handling here...
}

But note that you may have to consider - or + and white spaces as well.

So I'd actually prefer option 1.

answered Jun 14, 2020 at 22:23

Stephan Lechner

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4 Comments

ankitha shetty Over a year ago

Thank you so much.

HAL9000 Over a year ago

Both of those cases will accept the string "3mice" as the value 3. That may or may not be good enough for your purpose.

ankitha shetty Over a year ago

thankyou for replying that made me think of a new test case @HAL9000

dxiv Over a year ago

@HAL9000 That could be covered by checking sscanf(argv[1],"%d %c",&r,&c) == 1 where char c; would be another variable to catch any unwanted characters coming after the number.

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