why does strcmp() not work in my program?

Question

I am writing a program that takes multiple words as input and determines which word would come first and last if the words were listed in dictionary order. However my program does not fully work just yet.

Code:

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

void getword(void);

char str[20];
char smallest[20];
char largest[20];

int main(int argc, char *argv[]) {
    while (strlen(str) != 4) {
        getword();

        if (strcmp(str, smallest) < 0) {
            strcpy(smallest, str);
        } else
        if (strcmp(str, largest) > 0) {
            strcpy(largest, str);
        }
    }

    printf("smallest:%s\nlargest:%s\n", smallest,largest);

    return 0;
}

void getword(void) {
     printf("Enter a word: ");
     scanf("%s", str);
}

The user must enter words, I will assume the words are no longer than 20 characters long and if the user enters a 4 letter word then the program will stop.

The problem I have is that the first if statement (tests for smallest word in dictionary order) does not work. When the program is ran the output looks like this:

Enter a word: dog
Enter a word: zebra
Enter a word: rabbit
Enter a word: catfish
Enter a word: walrus
Enter a word: cat
Enter a word: fish
smallest:
largest:zebra

As you can see the 'smallest' word is not picked up and a simple printf statement in the if statement shows me that my program doesn't even enter the if statement at all, why is this?

Answer 1

There are multiple problems:

• you test the length of str before reading the word from the user, hence the 4 letter word will be handled.
• you should protect the scanf("%s", str) as scanf("%19s", str) to avoid buffer overflow if a word longer than 19 characters is entered.
• smallest is a global variable, thus is initialized as an empty string, so it is always smaller than any non empty input. You should avoid global variables.
• if a single word in input, it will be both the smallest and the largest word, hence you should not have an else statement or make a special case of the first word.

Here is a modified version:

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

// read a word from the user, return the word length
int getword(char *str) {
    printf("Enter a word: ");
    *str = '\0';
    scanf("%19s", str);
    return strlen(str);
}

int main(int argc, char *argv[]) {
    char str[20];
    char smallest[20] = "";
    char largest[20] = "";

    while (getword(str) != 4) {
        if (*smallest == '\0' || strcmp(str, smallest) < 0) {
            strcpy(smallest, str);
        }
        if (strcmp(str, largest) > 0) {
            strcpy(largest, str);
        }
    }
    printf("smallest:%s\n", smallest);
    printf("largest:%s\n", largest);

    return 0;
}

Answer 2

You are comparing str with smallest or largest. But the problem is smallest and largest are initialized to empty string(being declared as global). That means str may contain "Dog"/"Zebra"/"cat"/"anything" while smallest contains ""(empty string). In this case, (strcmp(str,smallest) < 0) will always be false. As a result smallest will always remain same and in the end, result will be smallest = "". Your program is doing right that and printing empty string as result of smallest.

What you can do is:

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

void getword(void);

char str[20];      //str = ""
char smallest[20]; //smallest= ""
char largest[20];  //largest = ""


int main(int argc, char *argv[])
{
    //>--------extra part begins-->---------------
    scanf("%s", smallest);
    strcpy(largest,smallest);
    //<--------extra part ends--<---------------

    while (strlen(str) != 4)
    {
      getword();

      if (strcmp(str,smallest) < 0)
      {
          strcpy(smallest,str);
      }

      else if (strcmp(str, largest) > 0)
      {
          strcpy(largest,str);
      }
 }

    printf("smallest:%s\nlargest:%s\n", smallest,largest);

    return 0;
}

void getword(void){
     printf("Enter a word: ");
     scanf("%s", str);
}