I'm having trouble with my conversion program - c++

Question

For my class, I am to write a program in C++ that converts each character in a sentence to the opposite case (upper to lower, lower to upper). We are supposed to use arrays and a user-defined method, and this is what I came up with:
#include <iostream>
using namespace std;
// declare variables
int count = 0; // array counter
int i = 0; // loop control
char ch[100]; // each character entered will be stored in this array
char newCh[100]; // this will hold each character after its case has been changed
main()
{
cout << "Enter a sentence." << endl; // prompts user
while ( ch[count] != '\n' ) // loop continues until "enter" is pressed
{
cin >> ch[count]; // store each character in an array
count += 1; // increment counter
}
int convert(); // call user-defined function
}
// even though it isn't necessary, we are using a user-defined function to perform the conversion
int convert()
{
for ( i = 0; i >= 0; i++ )
{
if ( (ch[i] > 64) and (ch[i] < 91)
)
{
newCh[i] = tolower(ch[i]);
}
else
{
newCh[i] = toupper(ch[i]);
}
cout << newCh[i];
}
}
I'm not sure why, but it doesn't work. I don't believe that my while loop is terminating and executing the rest of the program. Any advice would be greatly appreciated.

Answer 1

The loop condition in while ( ch[count] != '\n' ) is wrong, as all entries in ch will be initialized to zero by the compiler, and as you increase count inside the loop the condition will never be false and you have an infinite loop, causing you to write beyond the limits of the array.
And writing beyond the limits of an array leads to undefined behavior, and will cause your whole program to be illegal.
I suggest you learn about std::string and std::getline.

Answer 2

There's a problem with your for loop - you want for ( i = 0; i < count; i++ ). Also your function can be void and you need to pass the count value into it (and you just need to invoke it with convert() without int or void in front.

Answer 3

I have rewrite your code with some modification. The following code works perfectly in my machine -
#include <iostream>
#include<cstdio>
#include<string>
using namespace std;
void convert(char *, int);
string line;
char input[1024];
char output[1024];
main()
{
cout << "Enter a sentence." << endl;
while (getline(cin, line)) { // POINT 1
cout<< line<<endl;
//converting to char array since you need char array
//POINT 2
for(int i=0; i< line.length(); i++){
input[i]=line[i];
}
convert(input, line.length());
cout<<output<<endl;
input[1024] = {0}; //POINT 3
output[1024] = {0};
}
}
//Custom Convert Method
void convert(char input[], int size){
for(int i = 0; i < size; i++){
if(input[i] >= 'a' && input[i] <= 'z'){
output[i] = toupper(input[i]);
} else {
output[i] = tolower(input[i]);
}
}
}
Note some points (in my comment) here -
POINT 1: reading a n entire line using getline() method. Here line is a string
POINT 2: since you need char array here I am converting the string line to char array input[1024]
POINT 3: input and output array are being reset to work with the next value;
Output of the code:
"Ctrl+C" will terminate the program
Hope it will help you.
Thanks a lot.