Loop in C++: A Detailed Discussion with Examples

Loops in C ++: An Overview

What are loops in C++?

What is the need for Looping Statements in C++?

• Loops allow the user to execute the same set of statements repeatedly without writing the same code multiple times.
• It saves time and effort and increases the efficiency.
• It reduces the chance of getting errors during compilation.
• Loop makes the code readable and easier to understand, especially when dealing with complex logic or large data sets.
• It promotes code reusability.
• Loops help traverse data structures like arrays or linked lists.

Read More - C++ Interview Questions Interview Questions for Freshers

Types of Loops in C++

Syntax

for(initialization; testcondition; updateExpression)
{ 
//code to be executed 
} 

• Here, the initialization statement is executed first and only once.
• The testcondition is checked, if false the loop terminates
• If the testcondition is true, the body of the loop executes
• The update expression gets updated
• Again the testcondition is evaluated
• The process repeats until the testcondition becomes false.

Example in C++ Compiler

// Program to print numbers from 1 to 10
#include <iostream>
using namespace std;
int main() {
 for (int i = 1; i <= 10; i++) {
 cout << i << endl;
 }
 return 0;
}

• We know it will take 10 iterations to print 10 numbers so, we have used the for loop.
• i is initialized to 0.
• The condition i<10 will be checked. It is true, therefore i+1 i.e. 1 gets printed.
• Then i increments to 1 again the condition, i<10 is evaluated.
• The process will repeat until i become 10.

Output

1
2
3
4
5
6
7
8
9
10

2.) Nested for loop in C++

Example

#include <iostream>
using namespace std;
int main() {
 for (int i = 1; i <= 5; i++) {
 for (int j = 1; j <= i; j++) {
 cout << j << " ";
 }
 cout << endl;
 }
 return 0;
} 

• This C++ code generates a pattern of numbers using nested loops.
• The inner loop j iterates from 1 to the current value of i, printing numbers and spaces
• The outer loop i iterates from 1 to 5, regulating the number of rows.
• As a result, there is a pattern of numerals rising in each row, with a new line between each row.

Output

1 
1 2 
1 2 3 
1 2 3 4 
1 2 3 4 5 

3.) Infinite for loop in C++

Syntax

for(; ;) 
{ 
 // body of the for loop. 
} 

In the above syntax, there is no condition hence, this loop will execute infinite times.

Example

 #include <iostream>

int main() {
 for (;;) {
 std::cout << "Hello World" << std::endl;
 }

 return 0;
}

Hello World
Hello World
Hello World
Hello World
Hello World
... 

4.) for-each loop/ range-based for loop

Syntax

for (variableName : arrayName/vectorName) {
 // code block to be executed
}

Here, for every value in the array or vector, the for loop is executed and the value is assigned to the variable.

Example in C++ Editor

#include <iostream>
using namespace std;

int main() {
 int num[7] = {10, 20, 30, 40, 50, 60, 70};
 for (int i : num) {
 cout << i << "\n";
 }
 return 0;
}

Output

10
20
30
40
50
60
70

Summary