C toupper() function

C toupper(int c)

The toupper() function is used to translate lowercase characters to uppercase characters. The function is defined in the ctype.h header file.


int toupper(int ch);

toupper() Parameters:

Name Description Required /Optional
ch Argument ch represents a lowercase letter. Required

Return value from toupper()

  • Upon successful completion, toupper() returns the uppercase letter corresponding to the argument passed; otherwise returns the argument unchanged.

Example: C toupper() function

#include <stdio.h>
#include <ctype.h>
int main() {
    char ch;
     printf("Convert lower case to upper case:\n");
    ch = 'M';
    printf("%c -> %c", ch, toupper(ch));

    ch = 'k';
    printf("\n%c -> %c", ch, toupper(ch));
    ch = 'y';
    printf("\n%c -> %c", ch, toupper(ch));
    ch = 'w';
    printf("\n%c -> %c", ch, toupper(ch));
    return 0;


Convert lower case to upper case:
M -> M
k -> K
y -> Y
w -> W

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Previous C Programming: C tolower()

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C Programming: Tips of the Day

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An array "decays" into a pointer to its first element, so scanf("%s", string) is equivalent to scanf("%s", &string[0]). On the other hand, scanf("%s", &string) passes a pointer-to-char[256], but it points to the same place.

Then scanf, when processing the tail of its argument list, will try to pull out a char *. That's the Right Thing when you've passed in string or &string[0], but when you've passed in &string you're depending on something that the language standard doesn't guarantee, namely that the pointers &string and &string[0] -- pointers to objects of different types and sizes that start at the same place -- are represented the same way.

Ref : https://bit.ly/3pdEk6f