C programming - validating int input so it isn't a character

Question

Need to write a program to take input from a user in the form of an int and validate that what they entered is not a char from az.

Is there another way to do this other than:

if((num != 'a') && (num != 'b') && (num != 'c') && (num != 'd') etc.....) printf("You entered %d", num);

Answer 1

是的，使用ctype.h头文件中提供的isdigit（）函数

Answer 2

You can use the isalpha() function in the "ctype.h" header. It returns true if it is a letter. So you could do something like:

if ( !isalpha() )
{
    // Do whatever
}

Here is a link to the documentation for more information.

Answer 3

Rather than trying to work out that it's not a character, work out that it is a digit and discard the rest using the isdigit function from ctype like below.

#include <ctype.h>

...

if (isdigit(num)) {
  printf("You entered %d\n", num);
}

But this only works on single characters which is quite useless when you read in strings. So instead you could instead use the function sscanf. Like this.

int num;
if (sscanf(numstr, "%d", &num)){
  printf("You entered %d\n", num);
} else {
  printf("Invalid input '%s'\n", numstr);
}

Another option is to use the atoi function. But as I recall it doesn't handle errors and I find quite inferior to sscanf.

Answer 4

#include <stdio.h>
int main()
{
    char c;
    printf("Enter a character: ");
    scanf("%c",&c);
    if( (c>='a'&& c<='z') || (c>='A' && c<='Z'))
       printf("%c is an alphabet.",c);
    else
       printf("%c is not an alphabet.",c);
    return 0;
}