5

#include <stdio.h>
#include <stdlib.h>

int change_letter(char*);

int main()
{
    char slovo;
    printf("Unesite slovo : ");
    scanf("%c",&slovo);
    int x = change_letter(&slovo);
    printf("Rezultat je %c",x);

}

int change_letter(char *x){
    char novo;
    if(*x>='A' && *x<='Z'){
        novo = *x+32;
       }else if(*x>='a' && *x<='z'){
        novo=*x-32;
       }else{
       return NULL;}

           return novo;
       }