toupper() function in C

The toupper() function is used to convert lowercase alphabet to uppercase. i.e. If the character passed is a lowercase alphabet then the toupper() function converts a lowercase alphabet to an uppercase alphabet. It is defined in the ctype.h header file.
Syntax:

int toupper(int ch);

Parameter: It accepts a single parameter: 

• ch: This represents the character to be converted to uppercase.

Returns: This function returns the uppercase character corresponding to the ch.

Below programs illustrate the toupper() function in C:
Example 1:-

g in uppercase is represented as G

Example 2:-

GEEKFORGEEKS

Note: 

 If the character passed in the toupper() is any of these three

1. uppercase character

2. special symbol

3. digit

toupper() will return the character as it is.

Example :

Output:

GEEKS@123