Thread: Help on restricting input to a numbers only.

Below is the code I am using so far. Below code no problem but it was too long and less efficient.

Code:

#include <stdio.h>

    int main(void)
    {

        char dummy[50];
        int c_size[1], nFields;

        printf("Input class size (num of students): ", stdout);

            nFields = scanf("%d%1[^\n]", &c_size[0], dummy);

            while(1 != nFields || c_size[0] < 1)
            {
                printf("Invalid class size. Please try again.\n");
                fputs("\nInput class size (num of students): ", stdout);
                fflush(stdout);

                while(0 != scanf("%*[^\n]")); 

                nFields = scanf("%d%1[^\n]", &c_size[0], dummy); 
            }

    }

So, I wonder if anyone got a more good suggestion to restricting input to number only. Thanks you.

Code:

int num_students = -1;

do
   { printf("Number of students  : ");}
while (scanf("%d", &num_students) < 1 || num_students < 1);

Very thanks you ~ But could you explain to me what the purpose of num_students = -1 ?

It presets the number of students to an error value to make sure the loop repeats if the scanf() conversion fails.

First please view the code below.

Code:

#include <stdio.h>

    int main(void)
    {
        char ID[9];
               
        printf("Enter Student ID  : ");
        scanf("%[^\n]", &ID);
    }

I was trying to validate the student ID which should only allow 5 digits and 4 alphabets. E.g. 01234ADIA . I try to find code on line but no luck so far, so is it possible using c# to validate this?

You're going to have to write your own code to examine the student ID and check for the proper format.

Grab the thing as a string... check each position for correctness using isdigit() and isalpha()

Of course the correct format still doesn't mean it's a valid student ID... at some point you will need to check it against a list of ID's actually issued.

Code:

#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <conio.h> 
#include <stdlib.h>

int main (void)
{
  int i=0;
  char str[9];
  char a = 0;

    printf("ID: ");
    scanf( "%[^\n]", &str );

    if( isalpha(str[9]) == 1 ) {

        a++;

    }
     
    printf( "You entered %d alphabet\n", a);
    

  return 0;
}

Why I can't calculate number of alphabet by using above code? It always say 0?

Look up isalpha() in your C Library Documentation... See exactly what it does.