Question

Write a program that replace repeated three characters in a string by the character followed by 3. For example, the string aabccccaaabbbbcc would become aabc3ca3b3cc. When there are more than three repeated characters, the first three characters will be replaced by the character followed by 3. You can assume the string has only lowercase letters (a-z). Your program should include the following function: void replace(char *str, char *replaced);

Your program should include the following function:
void replace(char *str, char *replaced);

The function expects str to point to a string, replaced represents the string storing the replaced string. For example, if the str is helllo, the function will store hel3o in replaced.

1) Name your program repeated_chars.c.
2) Assume input is no longer than 1000 characters.
3) The replace function should use pointer arithmetic (instead of array subscripting). In other words, eliminate the loop index variables and all use of the [] operator in the function.
4) To read a line of text, use the read_line function (the pointer version) in the lecture notes.

MY CURRENT ISSUE:

I am having trouble with #3 of the assignment. "The replace function should use pointer arithmetic (instead of array subscripting). In other words, eliminate the loop index variables and all use of the [] operator in the function." How do I go about using pointer arithmetic to eliminate the loop index variables and all use of the [] operator in the function.

Here's what my code looks like:

#include <stdio.h>

#include <stdlib.h>

#define SIZE 1000

int read_line(char *str, int n);

void replace(char *str, char *replaced);

int main(){

char str[SIZE + 1];

char replaced[SIZE + 1];

printf("Please enter a word: ");

read_line(str, SIZE);

replace(str, replaced);

printf("Output: %s", replaced);

return 0;

}

void replace(char *str, char *replaced){

int i, j = 0;

// loop till end of the first line

for(i = 0; *(str + i) != '\0'; i++){

//check the first, second and third characters in the string

if((*(str + i) == *(str + (i + 1))) && (*(str + i) == *(str + (i + 2)))){

// replace the character

*(replaced + j) = *(str + i);

j++;

// assign 3 to the replaced string

*(replaced + j) = '3';

j++;

i += 2; // increment the index of the original string

}

else{

*(replaced + j) = *(str + i);

j++;

}

}

// terminates string

*(replaced + j) = '\0';

}

int read_line(char *str, int n){

int ch;

int i = 0;

while((ch = getchar()) != '\n'){

if(i < n){

*str++ = ch;

i++;

}

}

*str = '\0'; // terminates string

return i; // number of characters stored

}

Answer 1

#include <stdio.h>

void replace(char *str, char *replaced) {
        int count = 0;
        int lastChar = '\0';

        while(*str != '\0') {
                if(lastChar == *str) {
                        count++;
                } else {
                        if(count == 1) {
                            *replaced = lastChar;
                            replaced++;
                        } else if(count == 2) {
                            *replaced = lastChar;
                            replaced++;
                            *replaced = lastChar;
                            replaced++;
                        } else {
                                *replaced = lastChar;
                                replaced++;
                                *replaced = '3';
                                replaced++;
                        }

                        lastChar = *str;
                        count = 1;
                }
                str++;
        }

        if(count != 0) {
                if(count == 1) {
                    *replaced = lastChar;
                    replaced++;
                } else if(count == 2) {
                    *replaced = lastChar;
                    replaced++;
                    *replaced = lastChar;
                    replaced++;
                } else {
                        *replaced = lastChar;
                        replaced++;
                        *replaced = '3';
                        replaced++;
                }
        }
        *replaced = '\0';
}

int read_line(char *str, int n) {

        int ch;
        int i = 0;

        while((ch = getchar()) != '\n'){
                if(i < n){
                        *str++ = ch;
                        i++;
                }
        }
        *str = '\0'; // terminates string
        return i; // number of characters stored
}

int main(void) {
        char str[1000];
        char replaced[1000];
        printf("Enter input: ");
        read_line(str, 1000);

        replace(str, replaced);

        printf("\nEncoded:\n%s", replaced);

        return 0;
}