Loops in C

Loops are control structures that allow the execution of a block of code repeatedly as long as a specified condition is met.

Common types of loops in C are: for, while, and do-while.

• for Loop: Repeats a block of code a specific number of times. It is also known as Entry-Controlled loop as the condition is checked before the execution of code inside the loop body .

for.c

for (initialization; condition; increment/decrement) {
  // code block
}

---

• while Loop: Repeats a block of code while a condition is true. It is also Entry-Controlled loop

while.c

while (condition) {
  // code block
}

---

• do-while Loop: Executes code block at least once, then repeats while condition is true. It is also known as Exit-Controlled loop as the condition is checked after loop is executed

do-while.c

do {
  // code block
} while (condition);

---

Code Example

ex.c

  #include <stdio.h>

  int main(){
    printf("\n\n*******Loop in C*********\n\n");
    int index = 0;

    for(int j = 0; j <= 100; j++) {
      //FOR LOOP => A for loop is a repetition control structure that allows us to efficiently
      // write a loop that will execute a specific number of times.
      printf("%d\n", j);
    }

    while (index <= 10) {
      // WHILE LOOP => The while loop allows code to be executed multiple times, depending upon a
      // boolean condition. It is terminated on the basis of the Boolean (true or false) test condition.
      printf("%d\n", index);
      index++;
    }

    int j=0;
    do {
      printf("do while loop is running");
      // DOWHILE LOOP => 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.
    } while (j>5);
    // Note: In do-while loop, the loop body will execute at least once irrespective of the condition.

    return 0;
  }

Output

  *******Loop in C*********

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  do while loop is running

---

Note

You Should Know Something More

Nested Loop:

• A loop inside another loop.
• The inner loop runs completely every time the outer loop runs once.

nested.c

  #include <stdio.h>

  int main() {
    int i, j;

    // Outer loop for rows
    for (i = 1; i <= 5; i++) {

      // Inner loop for columns
      for (j = 1; j <= i; j++) {
        printf("* ");
      }

      printf("\n");  // Move to the next line
    }

    return 0;
  }

Output

  *
  * *
  * * *
  * * * *
  * * * * *

More Few Things

• An Infinite 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: When a break statement is encountered inside a loop whether it is a for loop or a while loop, the loop is terminated and the program continues with the statement immediately following the loop.

• continue statement: Using a continue statement in the loop will cause the control to go directly to the test-condition and then it will continue the loop process.

breakcont.c

  #include <stdio.h>

  int main() {
    for (int i = 1; i <= 10; i++) {
      if (i == 5) {
        continue;
      }

      if (i == 8) {
        break;
      }

      printf("%d ", i);
    }
    return 0;
  }

Output

1 2 3 4 6 7