Loop-Types in C++

February 17, 2023

Loops in C++

Here, in this section, we will discuss loops in C++. Loops help us automate repetitive work that we may have to do over and over again.

loops in C++

Loops discussed 

  • While loop
  • For loop
  • Do while
  • Nested loops

We will also learn more about the following as these are used in conjunction with loops

  • Switch statements
  • Jump Statements:
    • break
    • continue

While Loop

Imagine we had to print “Hello World” 100 times or n-number of times. Would it be wise to write cout << “Hello World\n” 100 times. While loops help us automate this.

Syntax

while(condition(s)){
    // execute statement(s)
}

Sometimes, the loop also uses an external initialization and incrementation logic to control how many times the loop may run

initialization;

while(condition(s)){
    // execute statement(s)
    incrementation;
}
loops in C++ new

Example

Run 
#include<iostream>
using namespace std;
 
int main()
{
    int i = 1;
    
    while(i <= 10)
    {
        cout << "Hello World, i:" << i << endl;
        i++;
    }
    
    return 0;
}

Output

Hello World, i:1
Hello World, i:2
Hello World, i:3
Hello World, i:4
Hello World, i:5
Hello World, i:6
Hello World, i:7
Hello World, i:8
Hello World, i:9
Hello World, i:10

For Loop

While loop uses an external variable to control the execution. A for loop takes into account the

  • Initialization
  • Condition checking
  • Incrementation

In its syntax itself. The syntax is shown below-

// initialization happens once before 1st iteration of loop
// condition checking happens everytime before new iteration
for(intialization ; condition(s); incrementation)
{
    
    // execution statements(s)
    
    // increment happens everytime as soon as current iteration completed   
}
Loops in C++ – 1

Example

Run 
#include<iostream>
using namespace std;
 
int main()
{
    int num = 5;
    
    // i = 1 is set once, before first running iteration
    // i <= 10 condition is checked before every new running iteration
    for(int i = 1; i <= 10; i++)
    {
        cout << num << " * " << i << " = " << (num * i) << endl;
        
        // i++ i.e. value of i is incremented before each iteration completes
    }
    
    return 0;
}

Output

5 * 1 = 5
5 * 2 = 10
5 * 3 = 15
5 * 4 = 20
5 * 5 = 25
5 * 6 = 30
5 * 7 = 35
5 * 8 = 40
5 * 9 = 45
5 * 10 = 50

Loop Types in C++

Decision Making in C++

Array in C++

String in C++

Function in C++

Do While Loop

  • Do while is very similar to while loop with one difference that it is exit control loop.
  • That is the decision to run the loop again or not happens at the time of exit of the current loop.
  • While in the while loop it happens before entry in the loop.

Syntax

do{
    // execute statement(s)
}
while(condition(s))

Sometimes when loop uses an external initialization and incrementation logic the syntax may look like –

initialization;

do{
    // execute statement(s)
    incrementation;
    
}while(condition(s))
Loops in C++ – 21

Example

Run 
#include<iostream>
using namespace std;
 
int main()
{
    int i = 1;
    
    do
    {
        cout << "Hello World, i:" << i << endl;
        i++;
    }while(i <= 10);
    
    return 0;
}

Output

Hello World, i:1
Hello World, i:2
Hello World, i:3
Hello World, i:4
Hello World, i:5
Hello World, i:6
Hello World, i:7
Hello World, i:8
Hello World, i:9
Hello World, i:10

Major difference between while and do-while

  • do-while loop run atleast once Since condition are checked later

Following do-while loop runs once and prints hello world once

Run

#include<iostream>
using namespace std;
 
int main()
{
    int i = 100;
    
    // do while runs atleast once
    do
    {
        cout << "Hello World, i:" << i << endl;
        i++;
    }while(i <= 10);
    
    return 0;
}

Output

Hello World, i:100

However, the following while loop doesn’t even run once

Run

#include<iostream>
using namespace std;
 
int main()
{
    int i = 100;
    
    // wont even run once as while is entry controlled
    while(i <= 10)
    {
        cout << "Hello World, i:" << i << endl;
        i++;
    }
    
    return 0;
}

Output

**Nothing is printed

Jump Statements

Now we will discuss jump statements which are 

  • Jump Statements:
    • break
    • continue

Break Statement

Whenever a break statement is encountered inside a loop (for or While or Do-while), the loop is immediately terminated and program control resumes at the next statement following the loop

for(init;conditions;increments){
    
    if(some condition(s)){
        // For loop immediately terminates
        // no matter if there are pending iterations
        break;
    }
}
// program flow will come here immediately
Decision making in C++ new – 4

Example

Run

#include<iostream>
using namespace std;

int main()
{
    // ideally should run 10 times b/w [1,10]
    for(int i = 1; i <= 10; i++){
        
        // whole loop terminates when i becomes divisible by 5
        if(i % 5 == 0)
            break;
    
        cout << "i: " << i << endl;
    }
}

Output 

i: 1
i: 2
i: 3
i: 4

Continue Statement

Whenever a continue statement is encountered inside a loop, the current iteration of the loop is skipped and the loop executes from the next iteration

for(init;conditions;increments){
    
    if(some condition(s)){
        // Current iteration of loop is skipped
        // Starts from next iteration
        break;
    }
}
// program flow will come here after loop completion

Example

Run 
#include<iostream>
using namespace std;

int main()
{
    // ideally should run 10 times b/w [1,10]
    for(int i = 1; i <= 10; i++){
        
        // Even iterations are skipped
        // it true then continue statement forces
        // loop to be started from next iteration
        if(i % 2 == 0)
            continue;
        
        // statements skipped if continue statement executes
        cout << "i: " << i << endl;
    }
}
 

Output

  
i: 1
i: 3
i: 5
i: 7
i: 9

Switch Case

It is ideal for whenever we can to merge a lot of if – else loops into multiple cases checking and executing unique statements if one of them is true. 

switch(expression) 
{
   case constant-expression1:
      // statement(s);
      break;
   
   case constant-expression2:
      // statement(s);
      break;
  
   // you can have any number of case statements
   default: // Optional but ideal
      // statement(s);
}
Decision making in C++ new – 3

Example

Run 
#include<iostream>
using namespace std;

int main()
{
  char op;
  int num1 = 20, num2 = 5;
  
  cout << "Enter operator either + or - or * or /: "; cin >> op;

  switch(op)
  {
    case '+': 
        cout << num1+num2;
        break;
    case '-': 
        cout << num1-num2;
        break;
    case '*': 
        cout << num1*num2;
        break;
    case '/':
        cout << num1/num2;
        break;
    
    //if case label not available example op = %
    default: 
        cout << "Select valid choice";
        break;
    }
}
 

Output

  
Enter operator either + or - or * or /: *
100

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