Thread: Replacing three 'a' in with a single '*' in a string

Unless you want to do a lot of swapping around, you need two arrays for this. For example:

Code:

for (i = 0, j = 0; i < 256; ++i, ++j) {
    if (buffer[i] == 'a' && buffer[i+1] == 'a' && buffer[i+2] == 'a') {
        buffer2[j] = '*';
        i += 2;
    } else {
        buffer2[j] = buffer[i];
    }

    putchar(buffer2[j]);
}

I meant that you have to move the rest of the array elements two places back each time you find a match. Like this:

Code:

if(buffer[i] == 'a' && buffer[i+1] == 'a' && buffer[i+2] == 'a') {
    buffer[i]= '*'; 
    for (j = i+3; j < 256; ++j) {
        buffer[j-2] = buffer[j];
    }
}

You don't need a second array and you don't need to move things around all the time either.

Code:

#include <stdio.h>

int main() {
    char b[256], c;

    int size = 0;
    while ((c = getchar()) != '\n') {
        if (size == 256) break;
        b[size++] = c;
    }

    int from = 0, to = 0;
    while (from < size) {
        if (from < size - 2 && b[from]   == 'a'
                            && b[from+1] == 'a'
                            && b[from+2] == 'a') {
            b[to++] = '*';
            from += 3;
        }
        else
            b[to++] = b[from++];
    }
    size = to;

    for (int i = 0; i < size; i++)
        putchar(b[i]);
    putchar('\n');

    return 0;
}

Or you could do it as you read in the line.

Code:

#include <stdio.h>

int main() {
    char b[256], c;

    int size = 0, acnt = 0;
    while ((c = getchar()) != '\n') {
        if (size == 256) break;
        if (c == 'a') {
            if (++acnt == 3) {
                b[size++] = '*';
                acnt = 0;
            }
        }
        else {
            for ( ; acnt > 0; --acnt) b[size++] = 'a';
            b[size++] = c;
        }
    }
    for ( ; acnt > 0; --acnt) b[size++] = 'a';

    for (int i = 0; i < size; i++)
        putchar(b[i]);
    putchar('\n');

    return 0;
}