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C toupper()

The toupper() function converts a lowercase alphabet to an uppercase alphabet.

The function prototype of the toupper() function is:

int toupper(int ch);

toupper() Parameters

The function takes a single argument.

  • ch - a character

Return value from toupper()

If an argument passed to toupper() is

  • a lowercase character, the function returns its corresponding uppercase character
  • an uppercase character or a non-alphabetic character, the function the character itself

The toupper() function is defined in the <ctype.h> header file.

Example: C toupper() function

#include <stdio.h>
#include <ctype.h>
int main() {
    char c;

    c = 'm';
    printf("%c -> %c", c, toupper(c));

    c = 'D';
    printf("\n%c -> %c", c, toupper(c));

    c = '9';
    printf("\n%c -> %c", c, toupper(c));
    return 0;


m -> M
D -> D
9 -> 9
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