C++ Write a for Loop That Prints Firstnumber

In computer programming, loops are used to repeat a block of code.

For example, let's say we want to show a message 100 times. Then instead of writing the print statement 100 times, we can use a loop.

That was just a simple example; we can achieve much more efficiency and sophistication in our programs by making effective use of loops.

There are 3 types of loops in C++.

• for loop
• while loop
• do...while loop

This tutorial focuses on C++ for loop. We will learn about the other type of loops in the upcoming tutorials.

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C++ for loop

The syntax of for-loop is:

          for (initialization; condition; update) {     // body of-loop  }        

Here,

• initialization - initializes variables and is executed only once
• condition - if true, the body of for loop is executed
  if false, the for loop is terminated
• update - updates the value of initialized variables and again checks the condition

To learn more about conditions, check out our tutorial on C++ Relational and Logical Operators.

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Flowchart of for Loop in C++

Flowchart of for loop in C++

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Example 1: Printing Numbers From 1 to 5

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

Output

          1 2 3 4 5        

Here is how this program works

Iteration	Variable	i <= 5	Action
1st	i = 1	true	1 is printed. i is increased to 2.
2nd	i = 2	true	2 is printed. i is increased to 3.
3rd	i = 3	true	3 is printed. i is increased to 4.
4th	i = 4	true	4 is printed. i is increased to 5.
5th	i = 5	true	5 is printed. i is increased to 6.
6th	i = 6	false	The loop is terminated

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Example 2: Display a text 5 times

          // C++ Program to display a text 5 times  #include <iostream>  using namespace std;  int main() {     for (int i = 1; i <= 5; ++i) {         cout <<  "Hello World! " << endl;     }     return 0; }        

Output

          Hello World! Hello World! Hello World! Hello World! Hello World!        

Here is how this program works

Iteration	Variable	i <= 5	Action
1st	i = 1	true	Hello World! is printed and i is increased to 2.
2nd	i = 2	true	Hello World! is printed and i is increased to 3.
3rd	i = 3	true	Hello World! is printed and i is increased to 4.
4th	i = 4	true	Hello World! is printed and i is increased to 5.
5th	i = 5	true	Hello World! is printed and i is increased to 6.
6th	i = 6	false	The loop is terminated

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Example 3: Find the sum of first n Natural Numbers

          // C++ program to find the sum of first n natural numbers // positive integers such as 1,2,3,...n are known as natural numbers  #include <iostream>  using namespace std;  int main() {     int num, sum;     sum = 0;      cout << "Enter a positive integer: ";     cin >> num;      for (int i = 1; i <= num; ++i) {         sum += i;     }      cout << "Sum = " << sum << endl;      return 0; }        

Output

          Enter a positive integer: 10 Sum = 55        

In the above example, we have two variables num and sum. The sum variable is assigned with 0 and the num variable is assigned with the value provided by the user.

Note that we have used a for loop.

          for(int i = 1; i <= num; ++i)        

Here,

• int i = 1: initializes the i variable
• i <= num: runs the loop as long as i is less than or equal to num
• ++i: increases the i variable by 1 in each iteration

When i becomes 11, the condition is false and sum will be equal to 0 + 1 + 2 + ... + 10.

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Ranged Based for Loop

In C++11, a new range-based for loop was introduced to work with collections such as arrays and vectors. Its syntax is:

          for (variable : collection) {     // body of loop }        

Here, for every value in the collection, the for loop is executed and the value is assigned to the variable.

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Example 4: Range Based for Loop

          #include <iostream>  using namespace std;  int main() {        int num_array[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};        for (int n : num_array) {         cout << n << " ";     }        return 0; }        

Output

          1 2 3 4 5 6 7 8 9 10        

In the above program, we have declared and initialized an int array named num_array. It has 10 items.

Here, we have used a range-based for loop to access all the items in the array.

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C++ Infinite for loop

If the condition in a for loop is always true, it runs forever (until memory is full). For example,

          // infinite for loop for(int i = 1; i > 0; i++) {     // block of code }        

In the above program, the condition is always true which will then run the code for infinite times.

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Check out these examples to learn more:

• C++ Program to Calculate Sum of Natural Numbers
• C++ Program to Find Factorial
• C++ Program to Generate Multiplication Table

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In the next tutorial, we will learn about while and do...while loop.

C++ Write a for Loop That Prints Firstnumber

Source: https://www.programiz.com/cpp-programming/for-loop

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