C++ Basics

1. C++ Basics Csci 107 Lecture 8

2. A C++ program //if necessary include headers //#include <foo.h> void main() { //variable declaration //read values input from user //computation //print output to user } Notes: • what follows after// on the same line is considered comment • indentation is for the reader; compiler ignores all spaces and new line ; the delimiter for the compiler is the semicolon • all statements ended by ; • Lower vs. upper case matters!! • Void is different than void • Main is different that main

3. Variable declaration type variable-name; Meaning: variable <variable-name> will be a variable of type <type> Where type can be: • int //integer • double //real number • char //character Example: int a, b, c; double x; int sum; char my-character;

4. Input statements cin >> variable-name; Meaning: read the value of variable <variable-name> from the user Example: cin >> a; cin >> b >> c; cin >> x; cin >> my-character;

5. Output statements cout << variable-name; Meaning: print the value of variable <variable-name> to the user cout << “any message “; Meaning: print the message within quotes to the user cout << endl; Meaning: print a new line Example: cout << a; cout << b << c; cout << “This is my character: “ << my-character << “ he he he” << endl;

6. If statements True False if (condition) { S1; } else { S2; } S3; condition S2 S1 S3

7. Boolean conditions ..are built using • Comparison operators == equal != not equal < less than > greater than <= less than or equal >= greater than or equal • Boolean operators && and || or ! not

8. Examples Assume we declared the following variables: int a = 2, b=5, c=10; Here are some examples of boolean conditions we can use: • if (a == b) … • if (a != b) … • if (a <= b+c) … • if(a <= b) && (b <= c) … • if !((a < b) && (b<c)) …

9. If example #include <iostream.h> void main() { int a,b,c; cin >> a >> b >> c; if (a <=b) { cout << “min is “ << a << endl; } else { cout << “ min is “ << b << endl; } cout << “happy now?” << endl; }

10. While statements True False while (condition) { S1; } S2; condition S1 S2

11. While example //read 100 numbers from the user and output their sum #include <iostream.h> void main() { int i, sum, x; sum=0; i=1; while (i <= 100) { cin >> x; sum = sum + x; i = i+1; } cout << “sum is “ << sum << endl; }

12. Arrays Used to store a collection of elements (variables) type array-name[size]; Meaning: This declares a variable called <array-name> which contains <size> elements of type <type> The elements of an array can be accessed as: array-name[0],…array-name[size-1] Example: int a[100]; //a is a list of 100 integers, a[0], a[1], …a[99] double b[50]; char c[10];

13. Array example //Read 100 numbers from the user #include <iostream.h> void main() { int i, a[100], n; i=0; n=100; while (i<n) { cout << “Input element “ << i << “: ”; cin >> a[i]; i = i+1; } //do somehing with it .. }

14. Problems Write a C++ program to read a sequence of (non-negative) integers from the user ending with a negative integer and write out • the average of the numbers • the smallest number • the largest number • the range of the numbers (largest - smallest) • Example: • The user enters: 3, 1, 55, 89, 23, 45, -1 • Your program should compute the average of {3, 1, 55, 89, 23, 45} etc