1. Department of Electronic & Electrical Engineering Statements Blocks{} Semicolons ; Variables Names keywords Scope

2. Department of Electronic & Electrical Engineering int x=5; int y=6; int z; z=x*2; x = y + z; printf("X"); Statements and semi colons. A statement is the smallest standalone element of a program. In C a statement must be terminated with a semicolon. examples: C ignores new lines and spaces (Very bad style but legal) declarations assignments function calls

3. Department of Electronic & Electrical Engineering Blocks and {} Curly brackets {} can be used to form a CODE BLOCK. Blocks are use to: Create a compound statement. Contain the body of a function. Blocks can be nested. { { } { } }

4. Department of Electronic & Electrical Engineering Compound Statements. if ( x>y) { printf(" x>y \n"); x=y; } Note that and if acts on a single statement if ( x>y) printf(" x>y \n"); x=y; /* not part of the if. Always executed. */

5. Department of Electronic & Electrical Engineering Function body void foo(int x, int y) { if ( x>y) { printf(" x>y " \n); x=y; } function body More about functions later...

6. Department of Electronic & Electrical Engineering Comments, Types Variables and Constants. { /* Declare some variables */ /*(must be at the start of a block) */ int i; float x,y,z; char c; /* Some assignment statement */ i=5; /* 5 is an integer constant */ x=2.0; /* 2.0 is a floating point constant */ y=3.0; c='X'; /* single quotes for a char */ z=x*y*4.0; /* x*y*4.0 is an expression */ } Comments delimited by /*.... */ Type Name Assignments Expressions

7. Department of Electronic & Electrical Engineering Demo: Run this with the debugger. int main() { /* Declare some variables */ /*(must be at the start of a block) */ int i; float x,y,z; char c; /* Some assignment statement */ i=5; /* 5 is an integer constant */ x=2.0; /* 2.0 is a float constant */ y=3.0; c='X'; /* single quotes for a char */ z=x*y*4.0; /* x*y*4.0 is an expression */ }

8. Department of Electronic & Electrical Engineering Examining variables using the debugger. Run the previous code to the i=5 line using the debugger A window appears showing the values of your variables. Note the variables are random values (whatever is in the memory). Step through the code and watch the values change!

9. Department of Electronic & Electrical Engineering Names for Variables and Functions In C you must declare variables/functions before they used. e.g. { int x; float z; ……. x and z are names.

10. Department of Electronic & Electrical Engineering Rules for Variable names Rules for constructing variable names Characters can be alphabets (a-z,A-Z), digits (0-9) and underscores ( _ ). Start with alphabet or underscore (not a digit). C keywords are not allow e.g. if for do int...

11. Department of Electronic & Electrical Engineering These keywords can not be used as names. All the keywords of the C language!

12. Department of Electronic & Electrical Engineering { int x; int z=4; x=3; { int x; /* a new variable */ int y=z; x=4; } /* what is x here ? */ y=5; } Declaring variables, nested blocks, scope. Hides the previous x BAD IDEA compile time error ! y does not exists here. The part of a program in which you can use a variable is called it's scope. you can see variables declared in a containing block.

13. Department of Electronic & Electrical Engineering Scope. Global: Variables declared outside functions can be seen every where (unless hidden by name reuse) Local: Variables declared within curly brackets are not visible outside the block. int x; /* global */ void main() { int x; /* local */ }

14. Department of Electronic & Electrical Engineering Statements smallest stand alone part of your code. Blocks{} create a compound statement from a number of other statements. Semicolons ; marks end of statements

15. Department of Electronic & Electrical Engineering Names labels for variables and functions Scope extent of a program in which a variable can be seen.