Conditional Statements: If, If-Else

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if() is a keyword in C++ which allows for conditional execution of code.



The syntax for the if statement is:

if (ConditionExpression){

ThenStatementBlock;

}

else {

ElseStatementBlock;

}

ConditionExpression contains the test expression. If the test expression evaluates to true (ie. non-zero), ThenStatementBlock is executed, otherwise the ElseStatementBlock is executed.

If there is more than one statement to be executed within the ThenStatementBlock or ElseStatementBlock branch, the blocks must be enclosed with {}'s.

It is not necessary to have an else statement within each if() conditional.

Multiple expressions can be evaluated by using conjunctions (e.g. &&, ||).

Indent your programs to increase readability.

Do not confuse the uses of assignment (=) and equality (==) operators, especially within the test condition. They can have adverse effects on your program.

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In some cases, a switch() statements can be used to simplify several nested if() statements.


Examples

MULTIPLE ELSE-IF COMPARISONS:






#include



int main()

{

// Obtain package information

double Weight, Length, Width, Height ;

cout << "Enter weight of package in kilograms: ";

cin >> Weight;

cout << "Enter length of package in meters: ";

cin >> Length;

cout << "Enter width of package in meters: ";

cin >> Width;

cout << "Enter height of package in meters: ";

cin >> Height;



double CubicMeters = (Length * Width * Height);



// else-if ladder to check package requirements and display appropriate message

if ((Weight > 27) && (CubicMeters > 0.1))

cout << "Rejected: Too heavy and too large" << endl;

else if(Weight > 27)

cout << "Rejected: Too heavy" << endl;

else if (CubicMeters > 0.1)

cout << "Rejected: Too large" << endl;

else

cout << "Package accepted" << endl;



return(0);

};


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