CPS1011. Program Structure {C};

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1 CPS1011 Program Structure {C};

2 Content Basic Constructs Statements Keywords Identifiers Operators Data Debugging CPS1011 2/18

3 Basic Constructs (i) Preprocessor directives e.g. #include <stdio.h> Text merge Function definitions int main(void) A special function: Program's entry point. Only one per executable! OS (program loader) needs to know from where to start execution int: return value type ( ) : parameters void: none in this case CPS1011 3/18

4 Basic Constructs (ii) Declaration statements Object_type object_identifier e.g. int num; Represents a storage are of a certain size and representation\encoding of variable content Symbolic identifier for a memory address 0x num 0xFFFFFF CPS1011 4/18

5 Basic Constructs (iii) int Keyword Part of C's vocabulary/syntax Symbolic identifiers Cannot be keywords Must start with an alphabetic character or _ Can include numbers But not special characters E.g. myvar1 or _myvar_2 but not 1var or 1 var or int CPS1011 5/18

6 Basic Constructs (iv) (Value) Assignment statements = The assignment operator E.g. 1 num1 = 1; (lvalue) ; completes the statement E.g. 2 num2 = num1 + 3; [arithmetic expression: evaluates prior to assignment] (rvalue) (constant) 0x (lvalue) num (rvalue) 0xFFFFFF CPS1011 6/18

7 Basic Constructs (v) lvalue (of a symbolic identifier) On the left hand side of = Represents the actual memory address rvalue (of a symbolic identifier) On the right hand side of = Represents the actual memory address Variable num1 Constant (literal i.e. not symbolic) 1 CPS1011 7/18

8 Basic Constructs (vi) Function call statements Function calls\usage E.g. printf("my favorite number is %d because it is first.\n",num); Readily available from standard library Requires #include <stdio.h> Arguments to match parameters 1 st A phrase enclosed in with data place holder %d (rest) data Reserved identifier do not use as your symbolic identifier! CPS1011 8/18

9 Basic Constructs (vii) Control statements Defines continuation of program which statement to execute next E.g. return 0; Back to statement prior to function call Or if in main(): Back to OS CPS1011 9/18

10 Basic Constructs (viii) Blocks Compound statements Logically grouped sequence of statements {. } E.g. Statement making up a function CPS /18

11 Basic Constructs (ix) Comments /* A comment Spanning multiple lines */ // A single line comment Not a statement! A note to the programmer Renders a program readable CPS /18

12 Basic Constructs (x) Listings 2.1, 2.2<<< CPS /18

13 Basic Constructs (xi) Function prototypes Function definition ending with a; Typically included in.h header files E.g. printf()'s prototype is located inside stdio.h Listing 2.3<<< CPS /18

14 Debugging (i) The process of eliminating software errors Can only be learned by practice! Soon you will notice that this process constitutes a hefty chunk of your programming effort Do not be discourage practice! CPS /18

15 Debugging (ii) Syntax error Not following C's grammar/vocabulary process Highlighted by Syntax checker Compiler error Listing 2.4<<< Semantic error Tricky Having the program not doing what is intended to do Listing 2.5<<< Others exist E.g. Memory corruption errors Source for several security breaches and crashes! Wait till we get to pointers... CPS /18

16 Debugging (iii) Dealing with semantic errors Trace the program state manually (dry run) Program state: variable value map Possibly changes per statement CPS /18

17 Debugging (iv) Alternatively Dump the program state with printf() Or best... use a debugger! Debug program Program State Breakpoints Stepping CPS /18

18 CPS1011 Reading List Textbook: C Primer Plus (6th edition). Stephen Prata. Addison Wesley, ISBN Supplementary reading: Expert C Programming: Deep C Secrets. Peter van der Linden. Prentice Hall, ISBN The C Programming Language. BW Kernighan, DM Ritchie. Prentice Hall, ISBN CPS /18

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