Validating input for numbers in c

Question

how can I validate user input for only entering numbers, if user entered something (string, character, etc) instead of number, it should show the error in. c programming language

@Blaze In general it is not recommended to use `scanf`. Too many things can go wrong. For example if this code is run in loop. — Eugene Sh., Oct 23 '19 at 14:53
[`strtod()`](https://pubs.opengroup.org/onlinepubs/9699919799/functions/strtod.html) ... `char *err; double value = strtod(input, &err); /* check errno, *err */` or use [`strtoull()`](https://pubs.opengroup.org/onlinepubs/9699919799/functions/strtoul.html) — pmg, Oct 23 '19 at 14:54
Don't use `scanf`. Use `fgets` and scan the string yourself using possibly `sscanf` or `strtod`, `strtol` etc. — Jabberwocky, Oct 23 '19 at 14:59
scanf may result in false positives, eg with `if (sscanf("42foo", "%d", &n) == 1) /* "42foo" accepted as number */;` — pmg, Oct 23 '19 at 15:00
Actually the `scanf` family of functions should only be used if you're sure the input format _actually_ matches the scanf format string. You can't be sure of anything with user input. — Jabberwocky, Oct 23 '19 at 15:08
Write a dedicated function, passing a prompt message, and the min/max acceptable values. — Weather Vane, Oct 23 '19 at 15:09
The second answer is usually my approach. Not familiar with the C99 functions in the first answer, but they certainly look useful: https://stackoverflow.com/questions/7021725/how-to-convert-a-string-to-integer-in-c?rq=1 — yano, Oct 23 '19 at 15:15

score -1 · Accepted Answer · edited Oct 23 '19 at 19:30

This program will find and gives error when it doesn't find any number in the input and it will specify the index in which the character is given as a input.

if you wanna declare the numbers you can by using a series of if-else conditions.

here I am basically differentiate the numbers and the character.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
    int i;
    char a[100];
    printf("enter the input value");
    replay:
    scanf("%s",&a);
    for(i=0;a[i]!='\0';i++)
    {


        if(a[i]=='1'||a[i]=='2'||a[i]=='3'||a[i]=='4'||a[i]=='5'||a[i]=='6'||a[i]=='7'||a[i]=='8'||a[i]=='9'||a[i]=='0')
        {

            printf("It Contains only numbers");

        }
        else
        {
            printf("\n error occured in %c position %d:\nEnter a valid number:",a[i],i);
            goto replay;
        }
    }
}

the if statement in 13th line of the code should be considered to be included the code — BalaSriRamanan, Oct 23 '19 at 18:06

Validating input for numbers in c

1 Answers1