c++ - swapping lower letters and upper letters -

#include <iostream>  using namespace std; int main(){    char letter,letter1;    cin>>letter;    char change_to_lower(letter);    char change_to_upper(letter);    char  swap(letter);    return 0; }  char change_to_lower(char a){     if(a=='a'&& a<='z'){         char b= toupper(a);         return b;     } }  char change_to_upper(char a){     if(a=='a'&& a<='z'){         char b = tolower(a);         return b;     } }  char  swap(char a){     char letter1,letter2;     a=change_to_lower(letter1);     char b=change_to_upper(letter1);     char temp = a;     a=b;     b=temp;     cout<< a<<" "<< b<<endl;     return b; } 

do mean convert uppercase characters lowercase characters , lowercase letters uppercase letters, in string?

void swapuplo(char *s) {     size_t i;      (i = 0; s[i]; ++i)         if (isupper(s[i]))             s[i] = tolower(s[i]);         else if (islower(s[i]))             s[i] = toupper(s[i]); } 

this calling routine

int main() {     char buf[] = "hello world";     swapuplo(buf);     printf("%s\n", buf);      getchar();     return 0; } 

output:

hello world 

be sure include <ctype.h>, contains declarations character testing functions.