implement strcat() function in C

Question

I'm trying to implement strcat() in C but stuck on that the output result is repeated src.

here is my code.


void my_strcat(char des[], char src[]) {
    int i = 0, j = 0;
    while (des[i] != '\0')
        i += 1;
    while (src[j] != '\0') {
        des[i + j] = src[j];
        j += 1;
    }
    des[i + j] = '\0';

    printf("%s", des);
}

int main() {
   char des[1000], src[100];
   for(int i = 0; i < 2; ++i) {
        printf("src: ");
        scanf("%s", src);
        my_strcat(des, src);
    }
    
    printf("%s", des);

}

the output is not the same as I was expected before. It's like for example:

src: a src: b des: aabb

my_strcat doesn't return anything, yet ou use its return value here: printf("%s", my_strcat(des, src)). Didn't you get at least c compiler warning? — Jabberwocky
– Jabberwocky, Commented Apr 1, 2021 at 13:38

Jabberwocky · Accepted Answer · 2021-04-01 13:49:18Z

1

You probably want this:

#include <stdio.h>
#include <stdlib.h>

void my_strcat(char des[], const char src[]) {   // better use const her
  int i = 0, j = 0;
  while (des[i] != '\0')
    i += 1;
  while (src[j] != '\0') {
    des[i + j] = src[j];
    j += 1;
  }
  des[i + j] = '\0';

  // printf("%s", des);  // dont print des here
}

int main() {
  char des[1000];
  char src[100];
  des[0] = 0;   // initialize des to a zero length string      
  for (int i = 0; i < 2; ++i) {
    printf("src: ");
    scanf("%s", src);
    my_strcat(des, src);
  }

  printf("%s", des);   // print the destination
}

answered Apr 1, 2021 at 13:49

Jabberwocky

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3 Comments

frankiie Over a year ago

Thank you so much! It worked. But please Could you explain why using printf() inside my_strcat() is not working?

Jabberwocky Over a year ago

@KeinKeinKein it is working, but it should not be there. After all your function is called my_strcat and not my_strcat_and_print_result

Olaf Dietsche Over a year ago

@KeinKeinKein The only relevant line is des[0] = 0;. When you initialize the destination, your example will work with or without the printf() call.

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