Check if a string has only numbers in C?

Question

I\'m trying to write a simple code to check if a string only has numbers in it. So far it\'s not working, any help would be appreciated.

#include          


        

Answer 1

Adding to the others answers, you can also use strtol to determine if a string has all numbers or not. It basically converts the string to an integer, and leaves out any non-integers. You can read the man page for more information on this function, and the extensive error checking you can do with it.

Also, you should use:

scanf("%9s", numbers);

Instead of:

scanf("%s", numbers);

To avoid buffer overflow.

Here is some example code:

#include 
#include 

#define MAXNUM 10
#define BASE 10

int main(void) {
    char numbers[MAXNUM];
    char *endptr;
    int number;

    printf("Enter string: ");
    scanf("%9s", numbers);

    number = strtol(numbers, &endptr, BASE);

    if (*endptr != '\0' || endptr == numbers) {
        printf("'%s' contains non-numbers\n", numbers);
    } else {
        printf("'%s' gives %d, which has all numbers\n", numbers, number);
    }

    return 0;
}

Example input 1:

Enter string: 1234

Output:

'1234' gives 1234, which has all numbers

Example input 2:

Enter string: 1234hello

Output:

'1234hello' contains non-numbers