Question

I have to try and use the GetSubstring function to print the result so that

printf(GetSubstring("character", 4, 3, resultArray));

outputs act

Limitations: can’t call other functions or macros, can’t add any other variables, can’t set variable to 0. Can only change function GetSubstring.

Here is my current code.

#include <stdio.h>
#include <stdlib.h>
char *GetSubstring(const char source[], int start, int count, char result[]);

int main(void)
{
const char source[] = "one two three";
char result[] = "123456789012345678";

puts(GetSubstring("character", 4, 3, result));

return(EXIT_SUCCESS);
}


char *GetSubstring(const char source[], int start, int count, char result[])
{
    char *copy = result;
    for (; *source != '\0' || *source == source[start]; start--)
    {
        while (*source != '\0')
        {
        *result++ = *source++;
        }

    }

    *result = '\0';
    return (copy);                                      // outputs character
    // return (result);                                 // outputs 012345678
}

Thank you for your help.

Answer 1

This line is supposed to terminate the string:

*result += '\0'

But it doesn’t because you are adding zero to the existing value. Try setting it to zero instead:

*result = '\0'

More importantly, your loop is wack. This contains a whole lot of recipes for trouble:

for (; *source != '\0' || *source == source[start]; start--)
{
    while (*source != '\0')
    {
        *result++ = *source++;
    }
}

Why don’t you begin at start, and then increment…

int i = 0;
const char *str = &source[start];

while( i < count && *str != '\0' ) {
    result[i++] = *str++;
}
result[i] = '\0';