#include <stdio.h>

int main() {

	void to_upper_case(char *);
	char letter;

	printf("Enter letter: ");
	letter = (char)getchar();

	to_upper_case(&letter);

	printf("In upper case: %c", letter);

	return 0;
}

void to_upper_case(char *c) {
	int within_bounds(int, int, int);
	if(within_bounds(*c, 'a', 'z')) {
		*c -= 32;
	}
}

int within_bounds(int x, int low, int high) {
	if(x >= low && x <= high) return 1;
	return 0;
}