Selection

What is selection?

In an algorithmic implementation, an instruction or block of instructions may be executed (or

not) with certain predetermined conditions.

Selection Syntaxes:

if

if (boolean expression) statement;

or

if (boolean expression) {

    statement1;

    statement2;           Block of statements

……

}

If boolean expression resulting is true, then the statement after the if will be executed.

if-else

if (boolean expression) statement1;

else statement2;

or

if boolean expression is true, then it will execute statement1,  otherwise, it will execute 

statement2.

nested-if

The if ... else statement executes two different codes depending on whether the test expression is true

or false. Sometimes a choice must be made among more than 2 possibilities.

The if ... else nested statement allows you to search for multiple test expressions and execute different

codes for multiple conditions.

if (boolean expression) statement1;

if (boolean expression) statement2;

if (boolean expression) statement3;

I

switch-case

This statement is used in exchange for IF-ELSE, when the nested number of levels is huge and hard

to read.

switch (expression) {

case constant1 : statements1; break; 

.

.

case constant2 : statements2; break;

default : statements;

}

The Switch statement evaluates an expression by looking for each case constant value. If an 

expression value is a constant case value, the related statement / s is executed. If nothing matches, the

default statement is executed.






?: Operator

The ?: operator is similar to If,  the difference is that ?: returns a value..



Example:



if(a > b)

max_value = a;

else

max_value = b;

can be written as

max_value = (a > b) ? a : b;









Go To and Label

There is still "go to" for C, but it is recommended to avoid using "go to" as it will confuse the users.



Syntax: 

goto label

 ……

label : 

 ……

There are 4 types of error that we usually found

Compilation error

caused by a syntax error

Link error

causes link error caused by no object code at the time of the link

Runtime error

error while running,caused by numeric operations such as: overflow, floating point overflow, division by zero, and so on.

Logical error

caused by incorrect logic

By :Steven

2201852132

Computer Science and Statistics