Syntax for lab 5

Key syntax elements for lab 5

The C++ features we will add for lab 5 are arrays and (as a special case) null-terminated character arrays.. (Refer back to the course notes or to the lab 4 syntax examples for refreshers on the syntax used earlier.)

Introductory C++ array syntax:

Declaring an array of a fixed size

// create an array of 10 doubles
const int ArrSize = 10;
double myArray[ArrSize];

Declaring and initializing an array simultaneously

// create and initialize an array of 3 floats
const int ASize = 3;
float arr[ASize] = { 10.5, 6.123, 3.14 };

Assigning/putting a value in one array position

myArray[4] = 1.0;  // put the value one in array position 4

Accessing/using a value in one array position

float x = arr[1]; // copy a value from array position 1 to variable x

Using a loop to access all the elements of an array

// put the value 0.5 in each position of the array
for (int pos = 0; pos < ArrSize; pos++) {
   myArray[pos] = 0.5;
}

Passing an array as a parameter to a function

// prototype for a function to print the contents of an array
void printArray(double arr[], int size);

// ... suitable call to the function from somewhere inside main
   printArray(myArray, ArrSize);

Chars, character arrays, cout, cin.getline, and the cstring routines

Creating a char array and effectively initializing it as empty by putting a null terminator ('\0') in the first position
const int Size = 256; char text[Size]; text[0] = '\0';
Copying a text string into an array (strcpy automatically puts the null terminator at the end)
char str[Size]; strcpy(str, "put this text in the array");
Copying the contents of str2 into str1 (both char arrays)
strcpy(str1, str2);
Concatenating the contents of str2 onto the end of str1
strcat(str1, str2);
Printing the contents of a null-terminated char array (e.g. str1)
std::cout << "the contents are: " << str1;
Using cin.getline to read a line of user text into a character array (up to the maximum size specified, and automatically putting in the null terminator)
const int MaxSize = 64; char str[MaxSize]; std::cout << "Please enter a line of text:"; std::cin.getline(str, MaxSize);
Using strlen to look up the length of a null terminated string (the number of characters before the null terminator)
int len = strlen(str);

Using strcmp to compare two character arrays' contents (sort of)alphabetically*:

   int result = strcmp(str1, str2);
   if (result == 0) {
      cout << "the two strings are the same, both are " << str1;
   } else if (result < 0) {
      cout << str1 << " is alphabetically before " << str2;
   } else {
      cout << str2 << " is alphabetically before " << str1;
   }

*In fact, the comparisons are based on the ascii values of the characters, which lists all the uppercase letters before all the lowercase letters, i.e. A < B < C ... < Z < a < b < ... < z. (In this ordering, the characters 0-9 come before the characters A-Z, and various punctuation symbols are scattered in between.)

Using cctypes' functions to look up what kind of characters are in a string

// assumes we used #include <cctype> earlier,
// and that str is null-terminated
void classifyChars(char str[])
{
    int pos = 0;
    while (str[pos] != '\0') {
       char ch = str[pos];
       std::cout << ch " is a";
       if (isdigit(ch)) {
          std::cout << " digit";
       } else if (isupper(ch)) {  // there is also an islower
          std::cout << "n uppercase alphabetic char";
       } else if (isalpha(ch)) {  // there is also an alnum for alpha-numeric
          std::cout << "n alphabetic char";
       } else if (isspace(ch)) {  // ... and there are quite a number of others ...
          std::cout << " whitespace character";
       } else {
          std::cout << " character of some other type";
       }
    }
}