c++basiccs.ppt

c++basiccs.ppt

• 1.
  C++ Basics CSci 107
• 2.
  A C++ program //includeheaders; these are modules that include functions that you may use in your //program; we will almost always need to include the header that // defines cin and cout; the header is called iostream.h #include <iostream.h> int main() { //variable declaration //read values input from user //computation and print output to user return 0; } After you write a C++ program you compile it; that is, you run a program called compiler that checks whether the program follows the C++ syntax – if it finds errors, it lists them – If there are no errors, it translates the C++ program into a program in machine
• 3.
  Notes • what followsafter // on the same line is considered comment • indentation is for the convenience of the reader; compiler ignores all spaces and new line ; the delimiter for the compiler is the semicolon • all statements ended by semicolon • Lower vs. upper case matters!! – Void is different than void – Main is different that main
• 4.
  The infamous Hello worldprogram When learning a new language, the first program people usually write is one that salutes the world :) Here is the Hello world program in C++. #include <iostream.h> int main() { cout << “Hello world!”; return 0; }
• 5.
  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;
• 6.
  Input statements cin >>variable-name; Meaning: read the value of the variable called <variable- name> from the user Example: cin >> a; cin >> b >> c; cin >> x; cin >> my-character;
• 7.
  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;
• 8.
  If statements if (condition){ S1; } else { S2; } S3; condition S1 S2 S3 True False
• 9.
  Boolean conditions ..are builtusing • Comparison operators == equal != not equal < less than > greater than <= less than or equal >= greater than or equal • Boolean operators && and || or ! not
• 10.
  Examples Assume we declaredthe 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)) …
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  If example #include <iostream.h> voidmain() { 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; }
• 12.
  While statements while (condition){ S1; } S2; condition S1 S2 True False
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  While example //read 100numbers 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; }
• 14.
  Exercise • Write aprogram that asks the user – Do you want to use this program? (y/n) • If the user says ‘y’ then the program terminates • If the user says ‘n’ then the program asks – Are you really sure you do not want to use this program? (y/n) – If the user says ‘n’ it terminates, otherwise it prints again the message – Are you really really sure you do not want to use this program? (y/n) – And so on, every time adding one more “really”.