Loops in C

For performing a set of rules repeatedly we use loop

To make our code efficient and mantainable we use loop for doing some repeating work.

If we want that while a condition is true the function should keep running

Advantages of using loops

Code reusability
Saves times
Less size
Traversing?

Basic Syntax

Loop starts → checks the condition → true - Execute loop , iteration increases/decrease. → false - exit the loop

Types of loops

Do while loop
While loop
for loop

Kinds of loop

Entry controlled loop →In entry controlled loops, the test condition is evaluated before entering the loop body. The For Loop and While Loop are an example of entry controlled loops.
Exit controlled loop → In exit controlled loops, the test condition is tested at the end of the loop. The loop body will execute at least once, whether the test condition is true or false. The do-while loop is an example of an exit controlled loop.

Do While Loop

In do-while loops, the execution is terminated on the basis of the test condition. The main difference between the do-while loop and while loop is that, in the do-while loop, the condition is tested at the end of the loop body, whereas the other two loops are entry controlled loops.

Note: In do-while loop, the loop body will execute at least once irrespective of the test condition.

A do-while loop is similar to a while loop, except the fact that it is guaranteed to execute at least one time. Unlike for and while loops, which test the loop condition first, then execute the code written inside the body of the loop, the do-while loop checks its condition at the end of the loop.

How does the do while loop work?

First, the body of the do-while loop is executed once. Only then, the test condition is evaluated
If the test condition returns true, the set of instructions inside the body of the loop is executed again, and the test condition is evaluated.
This looping process goes on until the test condition becomes false.
If the test condition returns false, then the loop terminates.

                

                    //basic structure
                    do {
                        //code to be executed
                    } while (condition);
                    
                    // sample code
                    int i = 0;
                    do {
                        i = i+1;
                        printf("%d",i);
                    } while (i<10);

                    

                            #include <stdio.h>
                            int main()
                            {
                                int num, index = 0;
                                printf("Enter a number : ");
                                scanf("%d", &num);
                            
                                do
                                {
                                    printf("%d\n", index + 1);
                                    index = index + 1;
                                } while (index < num);
                                return 0;
                            }

While loops

While loop is called a pre-tested loop. The while loop allows code to be executed multiple times, depending upon a boolean condition that is given as a test expression. While studying for loop, we have seen that the number of iterations is known, whereas while loops are used in situations where we do not know the exact number of iterations of the loop. The while loop execution is terminated on the basis of the Boolean (true or false) test condition.

Properties of while loop

A conditional expression written in the brackets of while is used to check the condition. The Set of statements defined inside the while loop will execute until the given condition returns false.
The condition will return 0 if it is true. The condition will be false if it returns any nonzero number.
In the while loop, we cannot execute the loop until we do not specify the condition expression.
It is possible to execute a while loop without any statements. This will give no error.
We can have multiple conditional expressions in a while loop.
Braces are optional if the loop body contains only one statement.

                

                    // structure
                    while (condition)
                    {
                        // code to be executed
                    }
                    
                    // code
                    int i = 0;
                    while (i < 30)
                    {
                        printf("%d\n", i);
                        i = i + 1;
                    }

For loop

The for loop is used to iterate the statements or a part of the program several times.
It is used to traverse(to go or travel across or over) the data structure like the arrays and linked lists.
It has a little different syntax than while and do while loops

The "For" Loop is used to repeat a specific code until a specific condition is satisfied. The for-loop statement is very specialized. We use for a loop when we know the number of iterations we want, whereas when we do not know about the number of iterations, we use while loop.

                

                    //stucture
                    for ( initialize counter ; test counter ; increment/decrement counter)
                    {
                        //set of statements
                    }
                    
                    //code
                    for(i=0;i<5;i++){
                        printf("%d");
                    }

initialize counter: It will initialize the loop counter value, i.e., i=0.
- The expression represents the initialization of the loop variable.
- We can initialize more than one variable in Expression 1. → for(i=0,j=0;i<5;i++)
- Expression 1 is optional → for(;i<5;i++)
test counter: It verifies whether the condition is true.
- It is a conditional expression. It checks for a specific condition to be satisfied. If it is not, the loop is terminated.
- It can have more than one condition. However, the loop will iterate until the last condition becomes false. Other conditions will be treated as statements. → for(;i<5,j<3;i++)
- It is optional but then it will become infinite loop so we use break statement
- Expression 2 can perform the task of expression 1 and expression 3. This is, we can initialize the variable as well as update the loop variable in expresssion 2 itself.
- We can pass zero or non-zero value in expression 2. However, in C, any non-zero value is true, and zero is false by default.
Increment/decrement counter: Incrementing or decrementing the counter.
- Expression 3 is used to update the loop variable
- We can update more than one variable at the same time. → for(;i<5;i++,j++)
- Expression 3 is optional.
Set of statements: Execute the set of statements.

Break Statement and Continue Statements

What is an infiinite loop?

An infinite loop also known as an endless loop occurs when a condition always evaluates to true. Usually, this is considered an error.

Sometimes, while executing a loop, it becomes necessary to jump out of the loop. For this, we will use the break statement or continue statement.

Break Statement

Used to bring the program control out of the loop
The break statement is used inside loops or switch statement.
Break statement can be used with
- Loops
- Switch

                        

                                #include <stdio.h>
                                int main()
                                {
                                    int i, age;
                                    for (i = 0; i < 10; i++)
                                    {
                                        printf("%d\nEnter your age : ", i);
                                        scanf("%d", &age);
                                        if (age > 10)
                                        {
                                            break;
                                            // but in case of nested loop, only one  is terminated, the outer loop keeps on looping
                                        }
                                    }
                                    return 0;
                                }

Continue Statement

Used to bring the program control to the next interation of the loop
The continue statement skips some code inside the loop and continues with the next interation.
It is mainly used for a condition so that we can skip some lines of code for a particular condition.
It forces next iteration in loop i.e. as break terminates the loop but continue forces the next iteration of the loop.

                        

                                #include <stdio.h>
                                int main()
                                {
                                    int i, age;
                                    for (i = 0; i < 10; i++)
                                    {
                                        printf("%d\nEnter your age : ", i);
                                        scanf("%d", &age);
                                        if (age > 10)
                                        {
                                            break;
                                        }
                                        else if (age < 0)
                                        {
                                            break;
                                        }
                                    }
                                    return 0;
                                }

C Programming