C++ overview

1. C++ overview CS113

2. Computer I/O CPU RAM Memory (HD) Gene Itkis CS112

3. From you to computer a.cpp: … x=5; … a.obj Linker C++ pre-proc + compiler a.exe Gene Itkis CS112

4. C++ program What you write

5. The rest is commentary • Comments • Line comment: //… • “Block” (multi-line) comment: /*…*/ //this is a comment to the end of the line str = “this line is not a comment”; /*and this too will be ignored by the the computer*/ printf (“%s”, str); Gene Itkis CS112

6. Wrappers • Headers #include <iostream> • Inserts the text from file iostream.h into the program • Header files can be your own “common blocks” or system dependent (come with the system Gene Itkis CS112

7. Headers header.h: int x; char c; … a.cpp: //main file int x; char c; … … x = 5; c = ‘a’; … a.cpp: //main file #include <header> … x = 5; c = ‘a’; … Gene Itkis CS112

8. The main thing int main() { … … // the program … } Gene Itkis CS112

9. Finally, Objects • Constants • 1, 27, -97 • 3.14, 6.02e23 • ‘a’, ‘1’ • true, false • “hello”, “123)(*^@#, - string” Gene Itkis CS112

10. Creating Objects • Integers • int x, y = -5; • long i, j; // usually same as int • short k; // -215 to 215–1 • Reals • float p=3.14; • double zp=3.1415926535897932384; • double avogadro=6.02e23; // = 6.02*1023 Gene Itkis CS112

11. More types of objects • Alphanumericals • char c=‘a’; • string s=“this is a @#& string”, ps; • Boolean • bool there_is_God = true, agnostic; In the above examples, note • multiple variables in one declaration • initialization Gene Itkis CS112

12. Object names • NO keywords (reserved words) • Names of types • Other C++ constructs • Variable names • Just about any alphanumeric string: x1_Z • Except keywords, some special chars, etc. • Use descriptive names Gene Itkis CS112

13. Existing objects: Operators • Assignment • x=x+5; // general: object = expr; • Arithmetic operators • The usual: -, -, +, *, / • x-z ; x = -5 • Less usual: % //remainder • 14/3 // quotient = 4 • 14%3 // remainder = 14 mod 3 = 2 Gene Itkis CS112

14. Who’s first • Precedence (highest first) • -(negation) • * / % • + – Gene Itkis CS112

15. Shorthand • x++ // x = x+1 • x += y; // x = x+y • x *= y; // x = x*y • x /= --y; // x = x/(y-1) // and y = y-1 • Do NOT over(ab)use shorthand • a source of bugs and confusion • last 2 examples above are bad style Gene Itkis CS112

16. Conversions • Implicit conversion – to more complex: • int + long // long + long • int + double // double + double • BUT 14/4 –> 3 !!! • Explicit conversion • i = int(3.14); // i=3 • i= static_cast<int>(3.14) // i=3, more C++ Gene Itkis CS112

17. Conversions • More explicit conversions • int i=14, j=4, r;double x;r=i/j; // r=3x=double(i)/j; // x=3.5 Gene Itkis CS112

18. Char integrity • Character object represented by integer char c=‘a’;c++; // c=‘b’c -= 32; // c=‘B’int i= c-16; // i=2c=‘5’;int j=c-’0’; // j=5string s, h=“hello”, b=“ “,w=“world”;s=h+b+w; //s=“hello world” Gene Itkis CS112

19. Being logical but boolish • Operators • and (&&), or (||), not (!) • Binary arithmetic • Bit-wise • And: & • Or: | • Not: ~ • XOR: ^ • Shift: << , >> • We’ll see examples of these later Gene Itkis CS112

20. Bools & Bins • Examples • bool learn=true, miss_test, fail;int mask=0xF0F0, donts, bits=0x1234;miss_test = !learn;fail = !learn || miss_test;mask = ~mask;donts = bits & (~bits);bits = bits & mask; • Result: fail=false; mask=0x0F0F; donts=0x0; bits=0x0204 Gene Itkis CS112

21. When to store • string s = “now”; // compile time init • s = “now”;// run time assignment • Watch out for using un-initialized objects! Gene Itkis CS112

22. Re-cap Objects • “Pre-existing” (atomic): • Constants • Types • Operators • Yours • Variables • Can now write very simple programs • Calculators, converters, etc Gene Itkis CS112

23. Where to now? • More objects • New kinds – classes • New “operators”– functions • Flow control • Conditionals • if/else • Iteration • while, do … while, for • Iteration with functions: recursion Gene Itkis CS112