Problem Set: C Strings

1. 1. char mystr{31];
   2. puts("enter a string: ");
      gets(mystr);
   3. printf("you entered: %s\n", mystr);
   4. printf("your string starts with %c\n", mystr[0]);
   5. int length;
      // this for statement finds the null byte so the loop doesn't
      // need a body; that's why the for statement ends with a semicolon
      for (length = 0 ; mystr[length] != '\0' ; length++);
      printf("your string contains %d characters\n", length);
   6. mystr[length] = '!';
      mystr[length+1] = '\0';
   7. for (i = 0 ; i < length ; i++)
         printf("%c\n", mystr[i]);
   8. printf("your string is: %s\n", mystr);

2.    char one[21], two[21];
      puts("enter two words: ");
      scanf("%s", one);
      scanf("%s", two);
      if (strcmp(one, two) < 0)
         printf ("your words are: %s and %s\n", one, two);
      else
         printf ("your words are: %s and %s\n", two, one);
   

3.    char one[21], two[21], three[21];
      puts("enter three words: ");
      scanf("%s", one);
      scanf("%s", two);
      scanf("%s", three);
      if (strcmp(one, two) < 0)
         if (strcmp(three, one) < 0)
            printf ("your words are: %s %s %s\n", three, one, two);
         else if (strcmp(three, two) < 0)
            printf ("your words are: %s %s %s\n", one, three, two);
         else
            printf ("your words are: %s %s %s\n", one, two, three);
      else
         if (strcmp(three, two) < 0)
            printf ("your words are: %s %s %s\n", three, two, one);
         else if (strcmp(three, one) < 0)
            printf ("your words are: %s %s %s\n", two, three, one);
         else
            printf ("your words are: %s %s %s\n", two, one, three);
   

4.    int countwords(char str[]) {
         int i;
         int numwords = 0;
         for (i = 0 ; str[i] != '\0' ; i++) {
            // every blank is the end of a word unless it comes before the first word
            if (str[i] == ' ' && i != 0)
               numwords++;
         }
         // i is now the position of the null byte; if there wasn't a blank at
         // the end of the string then we still need to count the last word
         if (str[i-1] != ' ')
            numwords++;
         return numwords;
      }
   

5.    char line[81];
      puts("enter a line: ");
      gets(line);
      printf("your line contains %d words\n", countwords(line));
   

6. int countvowels(char str[]) {
       int numvowels = 0;
       int i;
       for (i = 0 ; str[i] != '\0' ; i++) {
           if (str[i] == 'a' || str[i] == 'e' || str[i] == 'i'
                    || str[i] == 'o' || str[i] == 'u')
               numvowels++;
           else if (str[i] == 'A' || str[i] == 'E' || str[i] == 'I'
                    || str[i] == 'O' || str[i] == 'U')
               numvowels++;
       }

7.    // use backslashes to enter " inside a string (the backslash changes the
      // meaning of " to a character instead of using it to end the string
      puts("enter a line (enter \"end\" to end): ");
      gets(line);
      // strmcp returns 0 (false) if they are equal so this loop will run as long
      // as they are not equal
      while (strcmp(line, "end")) {
         printf("your line contains %d vowels\n", countvowels(line));
         puts("enter a line: ");
         gets(line);
      }
   

8. int mystrlen(char line[]) {
       int len;
   
       // stop loop at position of null byte, which is the length
       // no body needed for this loop
       for (len = 0 ; line[len] != '\0' ; len++);
       return len;
   }
   

9. void mystrcpy(char dest[], char source[]) {
       int i;
       for (i = 0 ; source[i] != '\0' ; i++)
           dest[i] = source[i];
   
       // i is position of null byte in source, copy it into dest
       dest[i] = '\0';
   }
   

10. void mystrcat(char one[], char two[]) {
        int i;
    
        // get length of one
        int len = mystrlen(one);
    
        // start at beginning of two and end of one
        // copy everything from two into one
        for (i = 0 ; two[i] != '\0' ; i++, len++)
            one[len] = two[i];
    
        // add null byte to the end of one
        one[len] = '\0';
    }
    




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