1. C Short Overview
Lembit Jürimägi

2. Compilation
Code written in C doesn’t run directly but needs to be compiled
Code itself may be cross-platform but a compiled executable is not
Compilers supplied by hardware vendors, operating systems, etc
Compiler may be separate or integrated to IDE
Compiler workflow:
Code preprocessed for macro replacement, conditional compilation, source inclusion (preprocessor)
Preprocessed code compiled to object code (compiler)
Object code assembled to machine language (assembler)
Machine language packaged into an executable (linker)

3. C Standards
Classic
ANSI C (C89/C90)
C99
C11

4. C Syntax Case-sensitive Limited list of reserved words
Sparse notation using single characters
Nonessential functionality delegated to libraries
Short code but hard to read

5. Reserved words (C89) Datatypes Type related Statements Other
char, double, enum, float, int, long, short, signed, struct, union, unsigned, void
Type related
auto, const, extern, register, static, typedef, volatile
Statements
break, case, continue, default, do, else, for, goto, if, return, switch, while
Other
main, sizeof

6. Variables Typed but support implicit type conversion
Defined as type followed by identifier
Identifiers consist of latin letters, numbers and underscore
Identifier must start with a lower-case or upper-case letter
Variable can be defined anywhere in code
By default the scope of the variable is limited to current block
If defined outside any block then it’s a global variable (try to avoid)
If identifier followed by [ ], then it’s an array

7. Built-in data types Type name Size Value range char, unsigned char
8 bits
, , ASCII characters
short, unsigned short,
short int, unsigned short int, (int)
16 bits
-32, ,767, ,535
long int, unsigned long int, (int)
32 bits
-2,147,483, ,147,483,647, ,294,967,295
long long int, unsigned long long int, (long int)
64 bits
-9,223,372,036,854,775, ,223,372,036,854,775, ,446,744,073,709,551,615
float
1.1 × 10− × 1038
double
2.2 x 10− x 10308
long double
80 bits
3.4 x x
void ?

8. Constants Integer constants Floating point constants Characters
12, 0x1F, 055 (decimal, hecadecimal, octal)
Stored as signed int unless specified otherwise (12l, 5u, 40ul)
Floating point constants
3.2, 14e3
Stored as double unless specified otherwise (1.4f, 2.7l)
Characters
'a'
Stored as char
Strings
"a"
Stored as character array

9. Examples
int a; // define 32 bit signed integer, value undetermined long long unsigned int k = 0xFFFFFFFFFFFFFFFFul; // define 64 bit unsigned integer and set to max value float f = 3.4; // define 32 bit float, assign value 3.4 f = 9 / 5; // f gets value 1, since both operands are integers! double x, y, z; // define 3 variables at once int M[2] = {1, 5}; // define int array, set M[0] to 1, M[1] to 5 char S[] = "Hello"; // define character array big enough to hold string constant "Hello" S[0] = 'J'; // replace first character with 'J'

10. Operators Arithmetic Bitwise Assignment Boolean Comparison
+, -, *, /, %, ++, --
Bitwise
~, &, |, ^, <<, >>
Assignment
=, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>=
Boolean
!, &&, ||
Comparison
<, <=, >, >=, ==, !=
Reference and dereference
&, *, [ ]
Conditional
? :

11. Operator precedence Operator Type () Parentheses ! Logical NOT ++ --
Increment, decrement
* / %
Multiply, divide, remainder
+ -
Add, subtract
<< >>
Shift (multiply by 2, divide by 2)
< > <= >=
Less, greater, less-equal, greater-equal
== !=
Equal, not equal
&
Bitwise AND ^
Bitwise XOR |
Bitwise OR
&&
Logical AND ||
Logical OR ?:
Conditional
=, ..
Assignment

12. Statements Conditional statements Loops
if, else, switch, case, default
Loops
while, do, for, goto, break, continue

13. If if (expression) statement; if(a < b) x = a;
if (expression) statement; else statement;
if(b < c)
x = c;
else

14. Switch switch(a){ case value: statement; break; default: statement; }
case 1: x = -1;
break;
case 2: y = 0;
default: x = 1; }

15. While while(expression) statement; do statement; while(expression);
while(i < 10)
i++;
a = 5;
while(a > 0){
printf("%d\n", a);
a--; }
a = -1;
do{
} while(a > 0);

16. For for(initialization; expression; statement) statement;
for(i = 0; i < 10; i++)
printf("%d\n", i);
i = 20;
for(; i; printf("%d\n", i--));

17. Functions
Function definition is similar to global identifier definition but identifier must be followed by parentheses
Parameters are passed by position, one way
At most single return value
To bypass these limitations pointers are used
A program must have main function
The return statement is used to return value and / or break program flow

18. Example
int sum(int a, int b){ int x = a + b; return x; } void switchIfSmaller(int *a, int *b){ if(*a >= *b) return; int x = *a; *a = *b; *b = x;

19. Libraries stdio.h for input output functionality
printf, scanf, fgets, fopen, feof, fclose
FILE datatype
stdlib.h for conversion and memory management
atoi, atof, malloc, realloc, free, qsort, rand
NULL constant
string.h for string operations
strcmp, strcpy, strlen, memcpy, memset
math.h for math
cos, sin, tan, acos, asin, atan, exp, log, pow, sqrt, ceil, floor, fabs
time.h for date and time functions
time
struct tm datatype