Loop

Loop in C

Written by: saeed1907057

Fri, 08 Nov 2024

Before going to the key example, have a look at the picture below:

next image

What do you understand from this picture?

The picture shows a process that repeats the same actions over and over, following the same path.
This is similar to loops in programming, where we run the same set of instructions multiple times.
Loops help us automate tasks by doing the same work again and again until a certain condition is met.
For example, imagine we want to count from 1 to 5. Instead of writing each number manually, we can use a loop to repeat the counting.

A for loop repeats a block of code a specific number of times based on the condition.
Syntax:
```
for (initialization; condition_check; update_state) {
   // body
}
```
- Initialization:
  - This is where we set up a starting point for our loop.
  - For example, int i = 0; would initialize i to start counting from 0.
  - It runs only once, at the beginning of the loop.
- Condition Check:
  - This part checks if the loop should execute the body part.
  - If this condition is true, the loop will continue to execute.
  - If it’s false, the loop stops.
  - For example, i < 10 would keep the loop going as long as i is less than 10.
- Update State:
  - This step changes the state or value of the loop variable each time the loop runs.
  - For example, i++ increases i by 1 after each loop cycle, moving it closer to the condition where the loop will end.
- Body:
  - This is the set of instructions that you want to run multiple times.
  - It’s the main part that executes repeatedly as long as the condition check is true.
- Initialization > Condition Check > Body > Update State > Condition Check > Body > Update State > ...
Have a look at this example.
```
for (int i = 1; i <= 5; i++) {
   printf("Hello World\n");
}
```
- This will execute the body of the loop 5 times, which means it will print "Hello World" 5 times in 5 lines.
- Output:
```
Hello World
Hello World
Hello World
Hello World
Hello World
```

A while is similar to for loop.
Only difference is initialization is done before loop, and increment is done usually at the end of body section.
If the condition is true, the loop continues; once it becomes false, the loop stops.

Syntax:

Initialization
while (Condition Check) {
   Body
   Update State
}

Example:

// Initialization
int i = 2;
while (i < 5) { // Condition Check
   // Body
   printf("Hello World\n");
   // Update State
   i++;
}

This will execute the body of the loop (4-2+1)=3 times, which means it will print "Hello World" 3 times in 3 lines.
Output:
```
Hello World
Hello World
Hello World
```

A do-while loop is similar to a while loop, but with one key difference: it guarantees the execution of the body section at least once regardless of the condition.
In a do-while loop, the code inside the body section is executed first, and then the condition is checked.
If the condition is true, the loop continues; otherwise stops.

Syntax:

Initialization;
do {
   Body
   Update State
} while (Condition Check);

Example:

int i = 2; // Initialization
do {
   // loop body
   printf("Hello World\n");
   // Update expression
   i++;
} while (i < 4); // Test expression

Useful when we want to stop the loop based on a certain condition within the body.

for (int i = 0; i < 10; i++) {
  if (i == 5) {
     break; // exit loop when i is 5
  }
  printf("%d\n", i);
}

continue skips the current iteration and moves directly to the next iteration of the loop.
Useful when we want to bypass certain parts of the loop body under specific conditions.

Example:

for (int i = 0; i < 10; i++) {
  if (i == 5) {
     continue; // skip iteration when i is 5
  }
  printf("%d\n", i);
}

0
1
2
3
4 //here 5 is not printed
6
7
8
9

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