How to Replace character in c++ without using library - c++

Question

I have prototype - int replace_char(string &, char);
I can't use library from string and ctype.h, I should write my own function.
So the task is to find in the text caharacter, which should I should replace with "*" .
example: In This is my text .
replace all t to * . Result will be - *his is my *ex*.
#include <iostream>
using namespace std;
int replace_char(string &, char);
int main ()
{
cout << ""Please insert text:"
cin >> str;
}
int replace_char(string str, char c1)
{
for (int i = 0 ; i < str.length(); i++)
{
if(str[i]==c1)
str[i]='*';
}
return str;
}

Answer 1

There were several errors in the code:
The function signature mismatches, the prototype is defined as std::string& but in the function definition, std::string only was used.
The program never converted the capital letter T or anything which is capital in order to convert them before comparing each letter with a single char.
The function is never used in the code.
cin >> str won't take longer texts followed by next whitespace character.
The function wants to return an integer, but actually returned type was a std::string, which is totally a misunderstanding.
The code redefined:
#include <iostream>
// taking a reference of std::string and a char
int replaceText(std::string&, char);
int main(void) {
std::string s;
int rep;
std::cout << "Enter a string: ";
std::getline(std::cin, s); // getline() to accept whitespaces
// since we're using a reference, the original variable is manipulated
int rep = replaceText(s, 't');
std::cout << "Output: " << s << std::endl;
std::cout << "Replaced number of chars: " << rep << std::endl;
return 0;
}
int replaceText(std::string& str, char c) {
size_t len = str.length();
static int count;
// changing each letter into lowercase without using any built-in functions
for (size_t i = 0; i < len; i++)
if (str[i] >= 'A' && str[i] <= 'Z')
str[i] = str[i] + 32;
// replacing the character, the main work
for (size_t i = 0; i < len; i++)
if (str[i] == c) {
str[i] = '*';
count++; // count a static variable
}
return count; // returning the overall counts
}
The program firstly takes an input from the user of type std::string and uses reference to the variable str. Now the program enters to the function code.
In the beginning, the function converts each letter to lowercase without using any library or a built-in function. Afterwards, it tries to compare each letter of the string carefully and as soon the given character matches a value containing in the string passed to the function, it replaces and counts a static variable which keeps the value save for the entire program life.
Thereafter, it simply displays the manipulated string.
It outputs something like:
Enter a string: This is a text
Output: *his is a *ex*
Replaced chars: 3

Answer 2

You seem to have a good start.
You need to declare str before reading input into it. Try string str;
Then you need to use your function in main. Either store its output into another string like string replaced = replace_char(str, 't');
Or put it into the output directly like cout << replace_char(str, 't') << endl;

Answer 3

Probably this is what you need
#include <iostream>
using namespace std;
int replace_char(string &, char);
int main ()
{
string str;
cout << "Please insert text:"
std::getline(cin, str);
int rlen = replace_text(str, 't')
cout << str << endl;
cout << "Number of replaced : " << rlen << endl;
return 0;
}
int replace_char(string str, char c1)
{
int rlen = 0;
for (int i = 0 ; i < str.length(); i++)
{
if(str[i]==c1) {
str[i]='*';
rlen++;
}
}
return rlen;
}

Answer 4

Given the prototype of the function, I'm guessing you need to return the number of chars replaced. This implementation should work:
#include <string>
#include <iostream>
using namespace std;
int replace_char(string &, char);
int main ()
{
cout << "Please insert text:";
string str;
getline(cin, str);
int nCharsReplaced = replace_char(str, 't');
}
int replace_char(string& str, char c1)
{
int count = 0;
for (int i = 0 ; i < str.length(); i++)
{
if(str[i]==c1)
{
str[i]='*';
count++;
}
}
return count;
}
Keep in mind there's no need to return the string, as you're passing it by reference, so the argument itself is modified.
Also, if you want the example you provided to work the replace_char functions cannot be case sensitive, since you replaced the capital 'T' with '*' too. In order to achieve that, you could implement a function that turns every char to lowercase (ideally, you would use tolower from ctype):
char to_lower_case(char c)
{
return c - ('Z' - 'z');
}
And replace the if condition with:
if (to_lower_case(str[i]) == c1)
If you don't understand how this work, take a look at how ASCII works.