Creating a function that concatenates two strings - c

Question

Create a function that concatenates two strings
The function should be created based on the following criteria
The putchar keyword should be used
The prototype must be char *_strcat(char *dest, char *src);
The function should add a terminating null value at the end of dest
The function should return a pointer to dest.
The function below finds the end of the src string and appends it to dest string.
I tried it out with my main.c file and got
World!Hello instead of Hello World!
void concatenate(char* str1, char* str2) {
int i = 0, j = 0;
// Find the end of the first string
while (str1[i] != '\0') {
i++;
}
// Append the second string to the end of the first string
while (str2[j] != '\0') {
str1[i] = str2[j];
i++;
j++;
}
// Add a null terminator to the end of the concatenated string
str1[i] = '\0';
}

Answer 1

Your assignment has problems:
Create a function that concatenates two strings.
This statement is not precise enough: should it allocate a new string or concatenate the second string at the end of the first string like strcat()?
The function should be created based on the following criteria.
I would rather write: The function should meet the following requirements.
The putchar keyword should be used.
This is a most ridiculous requirement! putchar is not a keyword, but a macro (an a function) defined in <stdio.h>. Using it in a user function is feasible, but tricky, not something newbies should be required to try and certainly not something any programmer should do.
The prototype must be char *_strcat(char *dest, char *src);
This requirement is bogus:
the identifier is a reserved word (it starts with an _). my_strcat or concat_string would be better choices
at least src should be declared const char *src. And it would indicate that the function likely behaves like strcat, or both arguments should be const qualified and the function should allocate memory.
The function should add a terminating null value at the end of dest.
This is implicit if the result is to be used as a C string.
The function should return a pointer to dest.
At last an indication regarding the expected semantics: the same as strcat.
Your implementation is almost correct, except for this:
the name is not as specified
the argument names are not dest and src
you should use size_t for the type of i and j
you must return dest.
Regarding your observations, you did not post the full program, but it is likely you passed the arguments in the wrong order and/or the destination array that contains Hello is not long enough to receive the concatenated string.
Here is a modified version:
#include <stdio.h>
char *my_strcat(char *dest, const char *src) {
size_t i = 0, j = 0;
#ifdef putchar
// just using the putchar identifier for fun
#endif
// Find the end of the first string
while (dest[i] != '\0') {
i++;
}
// Append the second string to the end of the first string
while (src[j] != '\0') {
dest[i] = src[j];
i++;
j++;
}
// Add a null terminator to the end of the concatenated string
dest[i] = '\0';
// return a pointer to dest.
return dest;
}
int main() {
char hello[20] = "Hello ";
char world[] = "World!";
printf("%s\n", my_strcat(hello, world));
return 0;
}