Control Statements

(if, if- else, switch statement, loops)

if Statement:

The if statement is implemented in two forms:

• Simple if statement
• if ... else statement

The Syntax of the two if statements are as follows:

if(expression){
    action 1;
       .
       .
       .
    action n;
}

if(expression){
    action 1;
       .
       .
       .
    action n;
}
else{
    action 1;
       .
       .
       .
    action n;
}

In the first case Simple if statement, if the expression under the if statement returns true or 1 then the the statements under if will execute else nothing will execute. 

In the Second case if-else statement, if the expression under the if statement returns true or 1 then the the statements under if will execute else the statements under the else will execute.

Example:

#include<iostream>
using namespace std;
int main(){
    x = 5;
    y = 20;
    z = 9;
    if(x == 5){
        cout << "x is equal to 5";       // Simple if Statement.
    }

    if(y > 10){
        cout << "y is Greater than 10";  // if-else statement.
    }
    else{
        cout << "y is smaller than 10";
    }

    if(z < 10){
        cout << "z is Greater than 10";  // if-else statement.
    }
    else{
        cout << "z is smaller than 10";
    }
    return 0;
}

output:

x is equal to 5
y is Greater than 10
z is smaller than 10

Switch Statement:

the switch statement is used to avoid the use of the if statement where a variable is compared many times. the syntax is as follows:

switch (n)
{
    case 1: // code to be executed if n = 1;
        break;
    case 2: // code to be executed if n = 2;
        break;
    default: // code to be executed if n doesn't match any cases
}

Important points to be remembered for Switch statement:-

• The expression provided in the switch should result in a constant value.
• Duplicate case values are not allowed.
• The default statement is optional.
• The break statement is used inside the switch to terminate a statement sequence. if it is not used then all the test cases will be executed, and we don't want that.
• Nesting of switch statements are allowed, which means you can have switch statements inside another switch.

Example:

#include <iostream>
using namespace std;
int main() 
{ 
   int x = 2; 
   switch (x) 
   { 
    case 1:
        cout << "Choice is 1"; 
        break; 
    case 2:
        cout << "Choice is 2"; 
        break; 
    case 3:
        cout << "Choice is 3"; 
        break; 
    default:
        cout << "Choice other than 1, 2 and 3"; 
        break;   
   } 
   return 0; 
}  

output:

Choice is 2

Loops:

There are three types of loops are available in C++

• do-while
• while
• for

do-while :-

it is an exit-controlled loop. based on the condition the control is transferred back to a particular point in the program, the syntax is as follows:

do{
    action 1;
       .
       .
       .
    action n;
}
while(condition is true);

Example:

#include<iostream>
using namesapce std;
int main(){
    int x = 1;
    do{
        cout << x << " ";
        x++;
    }
    while(x <= 10);   //output: 1 2 3 4 5 6 7 8 9 10
}

while :-

this is also an loop, but it is an entry-controlled loop, the syntax is as follows:

while(condition is true){
    action 1;
       .
       .
       .
    action n;
}

Example:

#include<iostream>
using namesapce std;
int main(){
    int x = 1;
    while(x <= 10){
        cout << x;     // output: 1 2 3 4 5 6 7 8 9 10
        x++;
    }
}

for:

The for is an entry controlled loop and is used when an action is to be performed for a predetermined number of times, the syntax is as follows:

for(initial value; test; increment/decrement){
    action 1;
       .
       .
       .
    action n;
}

Example:

#include<iostream>
using namesapce std;
int main(){
    int x;
    for(x = 1; x <= 1; x++){    //output: 1 2 3 4 5 6 7 8 9 10
        cout << x;
        x++;
    }
}