Character Type Header File
If you need to check what type of character the viewer typed, use ctype.h which is the character type header file. We write it like this: #include<ctype.h>
Here is a list of character type library functions:
| isalpha | checks if the input is an alphabetical letter | |
| isdigit | checks if the input is a number | |
| isupper | checks if the input is an upper case letter | |
| islower | checks if the input is an lower case letter |
Let’s examine each of these character type library functions.
isalpha: checks if the input is an alphabetical letter
To check whether the viewer types a letter or number, use isalpha. Here is the syntax:
- if the input is a letter, then isalpha != 0
- if the input is NOT a letter, then isalpha == 0
Here is an example:
| #include<stdio.h> #include<ctype.h> void main( ) { char letter; printf(“Type a letter: “); scanf(” %c”, &letter); if(isalpha(letter) == 0) printf(“You did NOT type a letter!”); else printf(“Your letter is %c.”, letter); } |
Type this source code in your editor and save it as alph.c then compile it, link it, and run it.
isdigit: checks if the input is a number
We can use isdigit the same way as isalpha. Here is the syntax:
- if the input is a number, then isdigit != 0
- if the input is NOT a number, then isdigit == 0
Here is an example:
| #include<stdio.h> #include<ctype.h> void main( ) { int year; printf(“What year is it? “); scanf(“%d”, &year); if(isdigit(year) == 0) printf(“You did NOT type a number!”); else printf(“The year is %d.”, year); } |
Type this source code in your editor and save it as dig.c then compile it, link it, and run it.
isupper: checks if the input is an upper case letter
If you want to check the case of a letter, use isupper.
- if the input is in upper case, then isupper != 0
- if the input is NOT in upper case, then isupper == 0
Here is an example:
| #include<stdio.h> #include<ctype.h> void main( ) { char first; printf(“What is the first letter of your name? “); scanf(” %c”, &first); if(isupper(first) == 0)printf(“You should capitalize the first letter of your name.”);else printf(“%c is the first letter of your name.”, first);} |
Type this source code in your editor and save it as up.c then compile it, link it, and run it.
islower: checks if the input is a lower case letter
This is the opposite of isupper.