The isupper()
function in C is a standard library function that checks if a given character is an uppercase letter. It is part of the C standard library (ctype.h
). This function is useful for determining if a character is an uppercase alphabetic letter.
Table of Contents
- Introduction
isupper()
Function Syntax- Examples
- Checking if a Character is an Uppercase Letter
- Using
isupper()
with User Input
- Real-World Use Case
- Conclusion
Introduction
The isupper()
function checks if a given character is an uppercase letter, meaning it is one of the characters from 'A' to 'Z'. This function is useful in various scenarios, such as validating user input or parsing text.
isupper() Function Syntax
The syntax for the isupper()
function is as follows:
#include <ctype.h>
int isupper(int c);
Parameters:
c
: The character to be checked, which is passed as anint
.
Returns:
- The function returns a non-zero value (true) if the character is an uppercase letter; otherwise, it returns 0 (false).
Examples
Checking if a Character is an Uppercase Letter
To demonstrate how to use isupper()
to check if a character is an uppercase letter, we will write a simple program.
Example
#include <stdio.h>
#include <ctype.h>
int main() {
char ch = 'G';
// Check if the character is an uppercase letter
if (isupper(ch)) {
printf("'%c' is an uppercase letter.\n", ch);
} else {
printf("'%c' is not an uppercase letter.\n", ch);
}
return 0;
}
Output:
'G' is an uppercase letter.
Using isupper()
with User Input
This example shows how to use isupper()
to check if a character provided by the user is an uppercase letter.
Example
#include <stdio.h>
#include <ctype.h>
int main() {
char ch;
// Get user input for the character
printf("Enter a character: ");
scanf("%c", &ch);
// Check if the character is an uppercase letter
if (isupper(ch)) {
printf("'%c' is an uppercase letter.\n", ch);
} else {
printf("'%c' is not an uppercase letter.\n", ch);
}
return 0;
}
Output (example user input 'A'):
Enter a character: A
'A' is an uppercase letter.
Output (example user input 'a'):
Enter a character: a
'a' is not an uppercase letter.
Real-World Use Case
Validating Uppercase Initials
In real-world applications, the isupper()
function can be used to validate that initials or other significant letters in a string are uppercase.
Example: Validating Initials
#include <stdio.h>
#include <ctype.h>
int main() {
char name[100];
int is_valid = 1;
// Get user input for the name
printf("Enter a name: ");
scanf("%s", name);
// Check if the first letter of each word is uppercase
for (int i = 0; name[i] != '\0'; i++) {
if (i == 0 || name[i - 1] == ' ') {
if (!isupper(name[i])) {
is_valid = 0;
break;
}
}
}
// Print the result
if (is_valid) {
printf("The name '%s' is valid.\n", name);
} else {
printf("The name '%s' is invalid. Each word must start with an uppercase letter.\n", name);
}
return 0;
}
Output (example user input name "John Doe"):
Enter a name: John Doe
The name 'John Doe' is valid.
Output (example user input name "john doe"):
Enter a name: john doe
The name 'john doe' is invalid. Each word must start with an uppercase letter.
Conclusion
The isupper()
function is essential for checking if a character is an uppercase letter in C. It is useful in various applications, particularly in fields like data validation and text processing, where it is necessary to ensure that characters belong to the uppercase alphabetic set.
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