Hi can you set this code the right way?

Question

//program to convert first and last letters of each word in a string to upper case
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int invert_case(char ch);
int main() {
char str[50];
fgets(str, 50, stdin);
int l= strlen(str);
printf("input= %s\n", str);
int count=0;
for(int i=0; i<=l; i++){
if(i==0 || i==l-1){
invert_case(str[i]); count++;
continue;
}
if(str[i]==32){
invert_case(str[i-1]);
invert_case(str[i+1]);
count++; continue;
}
}
printf("output= %s\nnumber of times invert_case() is called= %d", str, count);
return 0;
}

int invert_case(char ch){

if(ch>='a'&&ch<='z'){
ch= ch-('a'-'A');
}
return 0;
}
//The output is as below

input= hello how are you
output= hello how are you
number of times invert_case() is called= 5

//But the output expected is
HellO HoW ArE YoU
please help
@Gen300

Answer 1

you can change invert_case() to take pointer to char. Reason is when you pass char by value then the char you pass in is copied for function invert_case(). all changes are made to its local copy but no changes are made outside of invert_case().

so inside invert_case() ch will behave like local variable... there are two ways you can fix it. one is with pointer, the other is without.

Method 1:
void invert_case(char *ch)
{
if (*ch >= 'a' && *ch <= 'z')
*ch -= ('a' - 'A');
}

Method 2:
char invert_case(char ch)
{
if (ch >= 'a' && ch <= 'z')
ch -= ('a' - 'A');
return ch;
}

first method is easier. but you must change all invert_case() inputs to take an address:
invert_case(&str[i - 1]);
invert_case(&str[i + 1]);

if you do second method you must return the char and assign it to the string:
str[i - 1] = invert_case(str[i - 1]);

Answer 2

thankyou @Gen200