What's wrong with my code function to make strcat function in C?

Question

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

char wordsum(char FW[256],char SW[256]){
    int i;
    int j=strlen(FW);
    for (i=0;i<=strlen(SW);i++)
      FW[i+j+1]=SW[i];
    printf("%c",FW);
    return FW;
}

int main()
{
   char F[256];
   char S[256];
   printf("Enter the first word\n");
   gets(F);
   printf("Enter the Second word\n");
   gets(S);
   wordsum(F,S);
   return 0;
}

I don't know what is wrong with my code to make strcat function. I hope to find the answer.

Answer 1

I assume that the code is written to learn more about the C language. If so, may I present an alternative implementation which does not use strlen(). The intention is to present some of the really nice features in the language. It may be a bit complicated to wrap ones head around the first time, but IIRC the code can be found in K&R's book The C Programming Language.

Here we go:

char* mystrcat(char *dest, const char *src)
{
    char *ret = dest;

    while (*dest)
        dest++;

    while ((*dest++ = *src++))
        ;

    return ret;
}

The first while-loop finds the end of the destination string. The second while-loop appends the source string to the destination string. Finally, we return a pointer to the original dest buffer.

The function could've been even nicer if it didn't return a pointer.

void mystrcat(char *dest, const char *src)
{
    while (*dest)
        dest++;

    while ((*dest++ = *src++))
        ;
}

HTH

Answer 2

There are a few problems in your function, I've changed and commented them below:

char *wordsum(char FW[256],char SW[256]){      // correct function type
   int i;

   int j=strlen(FW); 

   for (i = 0; i <= strlen(SW); i++)
       FW[i+j] = SW[i]; //change 'i + j + 1' to 'i + j'

    printf("%s",FW); //change format specifier as you are printing string not character

    return FW;
}

Then dot forget to capture the returned pointer using a char* variable in the calling function (here main() )

char *result;
result = wordsum(F,S);
printf("\n%s\n", result);

Working example: https://ideone.com/ERlFPE

Answer 3

There are several mistakes in your code. They are:

1) A function can't return an array in C and you don't need to do so. Change the return type from char to void of wordsum and erase the line return FW;

2) You want to print a string, right? Format specifier for string is %s . So write printf("%s",FW); instead of printf("%c",FW); .

3) Do this: FW[i+j]=SW[i]; . Why did you add an extra 1 to i+j ? Just think logically.

4) Add header file for strlen() , it's <string.h> .

5) Erase those asterisk marks before and after FW[i+j]=SW[i]; .