How to use properly isalpha function regarding array of strings?

Question

I am trying to use isaplha() function in order to check every character of each string to be sure if it is alphabetic. But for some reason it does not work. Program always goes into printf() function despite of an argument of an if statement. It seems that everything is okay with the code:

#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define N 5

int main(void) 
{
    char string[N][50];
    int i,j;

    printf("Enter an array of N strings:\n");

    for(i=0;i<N;i++){
        gets(string[i]);
    }

    for(i=0;i<N;i++){
        for(j=0;j<50;j++){
            if(isalpha(string[i][j])){
                printf("\nIt should not work with numbers");
            }
        }
    }

    return 0;
}

A char needs to be cast to unsigned char for isalpha. Iterate only to strlen — Antti Haapala -- Слава Україні, Aug 01 '19 at 14:36
Also for the love of all that is good and holy, DO NOT USE `gets`! (Ever!) — Steve Summit, Aug 01 '19 at 14:37
Also you need a bit more logic. You're printing "it should not work with numbers" whenever you find a character that *is* alphabetic. What you want to do, I think, is print something (once) if *all* characters in one of the strings is alphabetic, or if at least one isn't. — Steve Summit, Aug 01 '19 at 14:40

score 0 · Answer 1 · answered Aug 01 '19 at 14:39

Here you are.

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

#define N   5
#define M   50

int main(void) 
{
    char string[N][M];

    printf( "Enter an array of %d strings:\n", N );

    for ( int i = 0; i < N; i++ )
    {
        fgets( string[i], sizeof( string[i] ), stdin );
        string[i][strcspn( string[i], "\n" )] = '\0';
    }

    for ( int i = 0; i < N; i++ )
    {
        const char *p = string[i];

        while ( *p != '\0' && !isalpha( ( unsigned char ) *p ) ) ++p;

        if ( *p != '\0') printf( "\n\"%s\" should not work with numbers", string[i] );
    }

    return 0;
}

The program output might look like

Enter an array of 5 strings:

12345
123A5
87654
8765B
Hello

"123A5" should not work with numbers
"8765B" should not work with numbers
"Hello" should not work with numbers

Take into account that the function gets is not a standard C function that is it is not supported any more by the C Standard.

And this check

        if(isalpha(string[i][j])){
            printf("\nIt should not work with numbers");
        }

must be placed outside the inner loop that must check only the characters of a string not of the whole character array.

How to use properly isalpha function regarding array of strings?

1 Answers1