1. Programming Languages and Paradigms
The C Programming Language

2. Components of a C program
A C program is a collection of function definitions, (global) variable definitions, declarations and compiler directives
Functions ( e.g., void push( char c ) { … } )
Variables ( e.g., int top; char Store[MAX]; )
Declarations ( e.g., void push( char c ); )
Compiler directives ( e.g., #define MAX 100 #include <stdio.h> )
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

3. C program compilation Single source Multiple source
prog.c => prog.o => prog.exe
prog.c must contain a function definition for main()
Multiple source
Compile step: prog1.c => prog1.o, prog2.c => prog2.o, prog3.c => prog3.o, …
Link step: prog1.o prog2.o prog3.o … => prog.exe
There should be only one main() definition found in all of the source programs
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

4. Built-in data types in C
int, char, float
Short and long versions of these data types
short, long, double, long double, …
Storage size/capacity of a variable of a given type is dependent on hardware and O/S platform
No explicit boolean type in C
Control structures that require conditions expect an int value
0 => false, non-zero => true
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

5. Variable declarations
Declaring a single variable: type varname;
Declaring multiple variables of the same type: type varname1, varname2, … ;
Variable name
Rules for identifiers: sequence of letters, digits, and underscores, but start with a letter/underscore
Variable scope
Global: outside of functions
Local: within functions
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

6. Operators Arithmetic Logical Others + - * / % grouping: ( )
+ - * / %
grouping: ( )
increment:
assignment: = += -= *= /= %=
Logical
&& || !
Others
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

7. Input/Output Output: through the printf function
printf( “hello, world” );
printf( “the price of %d calls is %5.2f pesos\n”, num_calls, num_calls*6.50 );
Input: through the scanf function
int val; scanf( “%d”, &val );
Takes input from the keyboard (white spaces are separators)
Type specifiers: %d – int, %f – float, %c – char, %s – string (numbers after % sign specify format)
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

8. Composite types Arrays Structures
Collection of elements of the same type
Declaration: type varname[integer-value];
Structures
Collection of elements of different types or with different names
Declaration: struct strname { field declarations… }; struct strname varname;
dot operator: varname.field
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

9. Pointers (to be discussed in detail in another slide set)
Address operator: & De-referencing operator: *
Pointers and arrays
Array names as addresses
Pointer arithmetic
Array access []
Dynamic allocation
malloc, free, NULL
Multi-dimensional arrays
Pointers and structures: the -> operator
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

10. Strings (to be discussed in detail in another slide set)
String: sequence of characters (stored in a character array)
The null (‘\0’) terminator
String literals ( e.g., “hello” )
String functions (<string.h>)
strcpy
strlen
strcmp
strcat …
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

11. Statements expression-statement block-statement
Expression followed by a semicolon
expr; where expr consists of variables, constants, operators, parentheses, function calls
block-statement
0 or more statements enclosed in { }
Variable definitions may precede statements { def def def … stmt stmt stmt … }
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

12. Statements (decision)
if-statement
Condition bounded by parentheses
Numeric expression expected in condition
Optional else clause
switch-statement
Can be viewed as a special kind of block
Has entry points (through the case labels) and exit points (through break; statements )
switch expression should be of ordinal type
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

13. Statements (loops) while-statement do-while-statement for-statement
Loop test at the beginning of the loop
Loop body may not be executed at all
do-while-statement
Loop test at the end of the loop
Loop body executed at least once
for-statement
for( expr1; expr2; expr3 ) stmt
Has an equivalent while-loop formulation
Used if there is an explicit loop control variable
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

14. Statements (others) break; continue; return-statement
Breaks out of the nearest enclosing loop or switch
continue;
Proceeds to the loop test
return-statement
return expr;
Provides value return by a function
Without expr (if return type is void), the statement simply causes control to be returned to the caller
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

15. Functions Function definition: Return type Name Parameters
Body (block)
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

16. Parameter Passing In C, all parameters are pass by value
Note: pointers and the address operator enable a function to update data outside of the function
But the parameter passed (the address) is still a value
Example: int val; scanf( “%d”, &val );
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

17. Definitions vs declarations
Variables
Definitions associate attributes (e.g., type and scope) and allocate space for the variable
Declarations just associate attributes
Functions
Definitions specify signatures and specify method details (statements)
Declarations just specify a method’s signature
There should be only one definition, but possibly many declarations for a variable/function
When are declarations needed?
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

18. Module Organization in C
Suppose mod.c is a module containing functions to be used by other C source files
A mod.h file contains function prototypes and #define directives
An #include directive is placed in the file using the module (i.e., #include “mod.h”). (Do you need to include it in mod.c?)
Modules can be separately compiled and then linked with other modules to produce an executable
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

19. Scope Names in a { … } block are limited to that block
Local variables
Formal parameters of a function are local to the function body/block
Declarations outside the functions are accessible from other functions
extern declaration: compiler permits use of variables before they are defined
static definition: variable use restricted to functions within file
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.

20. Library Functions The C standard library
I/O, math, string functions and others
Prototypes are in:
<stdio.h>
<math.h>
<string.h>
<stdlib.h> …
5/14/2019
Copyright 2008, by the authors of these slides, and Ateneo de Manila University. All rights reserved.