**`isupper()`** is a C library function that checks whether or not the character passed as a parameter is an uppercase letter.

# Library
```c++
#include<ctype.h>
```

# Syntax
Below is the declaration of `isupper()`,
```c++
int isupper(int ch);
```
where `ch` is the character to be checked. The return type of the function is `int`. 

>If the letter passed to the function is an uppercase letter, the function returns a non-zero value. Otherwise, the function returns zero.

# Alternative approach
An alternative approach (without using `isupper()`) to check whether or not a character is an uppercase letter is to check if the character lies between $65$ and $90$ (inclusive). 

>If the character lies between $65$ and $90$ (inclusive), it is an uppercase letter. Otherwise, it is not. 


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

int main() {
  char str[] = {'a', '!', '2', 'M'};

  int i = 0;
  while (i < 4) {
    int returnValue = isupper(str[i]);
    if (returnValue > 0)
      printf("%c is an uppercase letter.\n", str[i]);
    else
      printf("%c is not an uppercase letter.\n", str[i]);
    ++i;
  }

  return 0;
}

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

int main() {
  char str[] = {'a', '!', '2', 'M'};

  int i = 0;
  while (i < 4) {
    if (str[i] >= 65 && str[i] <= 90)
      printf("%c is an uppercase letter.\n", str[i]);
    else
      printf("%c is not an uppercase letter.\n", str[i]);
    ++i;
  }

  return 0;
}

What is isupper() in C?

isupper() is a C library function that checks whether or not the character passed as a parameter is an uppercase letter. Library #include  Syntax Below is the declaration of isupper(), int isupper(int ch);  where ch is the character to be checked. The return type of the function is int.  If the letter passed to the function is an uppercase letter, the function returns a non-zero value. Otherwise, the function returns zero.  Alternative approach An alternative approach (without using isupper()) to check whether or not a character is an uppercase letter is to check if the character lies between 656565 and 909090 (inclusive).  If the character lies between 656565 and 909090 (inclusive), it is an uppercase letter. Otherwise, it is not.  

What is isupper() in C?

Library

Syntax

Alternative approach

Code

1. With `isupper()`

2. Without `isupper()`

What is isupper() in C?

Library

Syntax

Alternative approach

Code

1. With isupper()

2. Without isupper()

1. With `isupper()`

2. Without `isupper()`