C Basics

High-level view of programming

• Compile the source code
  - Compilation : converting the source code into machine code
• Run or Execute the machine-language file

A simple C program

#include <stdio.h>
int main()
{
	printf("simple C program");
    return 0;
}

• comments
  - /* *\/ & ignored by computer, describe program
• #include <stdio.h> (standard input/output operation)
  preprocessor directive

Variable

variables

• store/retrieve data
• type of variable determines what can be placed
• Assignment : placing a valude in a variable
• variable must be declared before they are assigned
• variable : flexible <-> constant : same value

naming variable

• reflect the role of variable
• begin with a letter(digitx), can contain digit, underscores

variable Declartation

must be declared before the first executable statment

main(){
	int a, b, c;
    float d;
}

• var_type var_namel
  -int age;
  • float annual_salary;
  • double weigh, height / multiple vars ok/

variable assignment

declaration - > assignment
float a,b;
int c;
b=2.12;
c=200;

• Using the "=" operator
  int age= 52; //joint declaration/assignment
  double salary;
  salary= 150000.23;
  age =53; //value may change at any time

C Data Types

char

• single byte(8bits)
• signed or unsigned
• internally char is just a number
• ASCII character set used in ANSI C

int

• signed interger of 4 or 8 bytes(32 or 64 bits)
• precise size is machine-dependent

float and Dobule

• 32 bit / 64 bit real numbers
• precise size depend on the architecture
  -int : integer of unspecified size
  -float : single-precision floating point (32)
  -double : Double-precision floating poing (64)

Additional...

• short, long, signed, unsigned
• machine-specific

Structure of a C program

/* description of program */
#include <stdio.h>
/*any other includes go here*/
int main(){
/*program body*/
return 0;
}

Statements

• end with a semicolon
• comma : separate multiple declaration
• blank lines have no effect
• extra spacese between tokens has no effect
• comments are ignored by the compiler

Executable Statements

• variable declaration/initialization
• not a declaration
  -Assignment statements
  -Arithmetic statements
  -Print statements

Printf() examples

• output to standard out -screen
• printf("%s\n","Hello world");
  : %s-> as a string, \n ->newline
• printf("%d\t%d\n",j,k);
  : j as an integer(%d), \t->tap
  k as an integer(%d), \n->new line
• printf("%f : %f : %f\n,x,y,z);
  : floating point variable x, followed by a space, colon, space

Invisible character \n : newline \t : horizontal tab

scnaf function

• in <stdio.h>
• scanf(format-specifier, &var1, &var2, etx);
  int a; scanf("%d", &a);
  double x; scanf("%f", &x);

While loops

• repeating a statement
• while(expr)
  {
  statement1;
  statement2;
  ......
  }
  if expr == true, preform statement....
  otherwiser, skip to end of while block

Operator

Arithmetic

1. + "plus" -> c= a + b
2. - "minus" -> c = a - b
3. * "times" -> c = a*b
4. / "divided by" c = a / b
5. % "modulus" c= a % b

Relational

1. > "greater than"
2. < "less than"
3. >= "greater than or equal to"
4. <= "less than or equal to"

Equality

1. == "is equal to"
2. != "is not equal to"

Logical

1. || "logical or"
2. && "logical and"

logical operator, cont
1. if((a==1)&&(b<3)||(c==1))