Question

• strcpy
• strcat
• strcmp
• strstr
• strchr
• fgets

Specification

The program should repeatedly prompt the user to enter a string of no more than 20 characters. The program will end when the user types in DONE (all caps). Use fgets to get input from the user.

Because fgets leaves the newline character on the string, the program should trim off the newline by replacing it with the null character, effectively shortening the string. Use strchr to locate the newline.

The program will use the input to build up a longer string. You may assume this string will be no longer than 1000 characters. The user input is compared to the longer string and then takes action as follows:

• If the input is contained within the longer string, ignore it. Use strstr to perform the search.
• If the user input is less than the longer string (as indicated by the return value from strcmp), prepend the input onto the longer string with a space separating them.
• If the input is greater than the longer string, append it with a space separating them.

After each user input, display the longer string.

Sample Run

Here's a sample of how the program would work. I've shown user input in bold, just to help it stand out. Your program won't use any special typography.

Enter a string: hello
hello
Enter a string: world
hello world
Enter a string: bye
bye hello world
Enter a string: cat
bye hello world cat
Enter a string: worl
bye hello world cat
Enter a string: beep
beep bye hello world cat
Enter a string: bingo
beep bye hello world cat bingo
Enter a string: DONE
beep byte hello world cat bingo

Let's analyze this one input at a time.

1. User enters hello. Since this is the first sting entered, it is copied into the longer string.
2. User enters world. Because world comes after hello, it is appended onto the longer string.
3. User enters bye. This comes before hello world, so it is prepended.
4. User enters cat. This comes after bye hello world, and is appended.
5. User enters worl. This string is found within the longer one; no change to the longer string.
6. User enters beep. Since beep comes before bye hello world cat, it is prepended.
7. User enters bingo. This comes after beep bye hello world cat, and is appended.
8. User enters DONE. The longer string is displayed one last time and the program ends.

Please note that the program is not putting the words in alphabetic order. It's actually doing something simpler than sorting.

Answer 1

#include <stdio.h>
#include <string.h>

int main()
{
    //Define a variable for input and output string*/
    char input[20];
    char output[1000] = "";

    // loop for getting input string
    while(1)
    {
        printf("Enter a string: ");
        // read input string
        if (fgets(input, sizeof(input), stdin) == NULL)
        {
            printf("Fail to read the input string");
        }
        else
        {
            //find new line
            char *ptr = strchr(input, '\n');
            if (ptr)
            {
                //if new line found replace with null character
                *ptr = '\0';
            }
        }

        // if input is DONE exit loop
        if (strcmp(input, "DONE") == 0)
            break;

        // If the input is contained within the longer output, ignore it and restart loop
        if(strstr(output, input)!=NULL )
        {
            printf("%s\n", output);
            continue;
        }

        // if input is the first sting entered, it is copied into the output string
        else if(strlen(output)==0)
            strcpy(output, input);

        // else if input is greater than the output string , append the input onto the output string with a space separating them.
        else if(strcmp(output, input)<0)
        {
            strcat(output, " ");
            strcat(output, input);
        }

        // else if input is less than the output string , prepend the input onto the output string with a space separating them.
        else if(strcmp(output, input)>=0)
        {
            strcat(input, " ");
            char temp[1000] = "";
            strcpy(temp, input);
            strcat(temp, output);
            strcpy(output, temp);
        }

        printf("%s\n", output);

   }
   return 0;
}

Output