write C language about greatest common divisor

Question

write about the greatest common divisor using c language. How can I put a "please entre positive number" statement when I typing a negative or float number in this code?

# include <stdio.h>

int GCD (int a, int b) {

    while ( b != 0 ) { 
              if ( a > b ) {
             a = a – b ;
          } else {
            b = b – a ;
         } return a;
          }

    int main (void) {
        int a, b,  result ;

        printf(“Type two positive integers”);
        scanf( %d %d, &a, &b);

        result = GCD ( a, b) ;
        printf(“GCD (%d, %d) = %d \n” , a , b, result );

        return 0;

    }

Welcome to SO! It looks like this was edited or copy-pasted from a rich text editor like a word document. Can you format it in plain text? — ggorlen, Nov 24 '19 at 00:42
in `GCD` you know how to test if `a` is greater than `b`, but dont know how to test if a number is less than zero? — yano, Nov 24 '19 at 00:47
Please revise the question title. It has nothing to do with GCD. It's about validation. Consider doing a search on input validation, and using fgets/sscanf instead of simple scanf, if you HAVE to implement validation. — dash-o, Nov 24 '19 at 06:59

artm · Answer 1 · 2019-11-24T06:16:25.000

2

How can I put a "please entre positive number" statement when I typing a negative or float number in this code?

You can check the values of a and b and repeated the scanf when either of them are not positive values:

while( ( 2 != scanf( "%d %d", &a, &b) ) || (a < 0 || b < 0) )
{
    printf("Error: please enter two positive numbers\n");
    continue;
}

edited Nov 24 '19 at 06:16

answered Nov 24 '19 at 00:43

artm

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This will not work because `scanf` accepts negative numbers for the `%u` format. Per C 2018 7.21.6.2 12, `u` “Matches an optionally signed decimal integer,…” The code `#include ` / `int main(void) { unsigned x; printf("Return value of scanning a negative number with %%u is %d.\n", sscanf("-3", "%u", &x)); }` shows the return value is 1. – Eric Postpischil Nov 24 '19 at 00:57
1

maybe just a simple check on the values themselves would do – artm Nov 24 '19 at 01:07
@chux-ReinstateMonica that makes sense, thanks – artm Nov 24 '19 at 06:16

write C language about greatest common divisor

1 Answers1