Loops

A loop is a programming tool that is used to repeat a set of instructions. Iterate is a generic term that means “to repeat” in the context of loops. A loop will continue to iterate until a specified condition, commonly known as a stopping condition, is met.

For Loop

A for loop begins with the for keyword and a statement declaring the three parameters governing the iteration, all separated by semicolons;:

• The initialization defines where to begin the loop by declaring (or referencing) the iterator variable.
• The condition determines when to stop looping (when the expression evaluates to false).
• The increment statement updates the iterator each time the loop is completed.

for (initialization; condition; increment) {
  // Code to be executed repeatedly
}

For example:

for (int i = 0; i < 4; i++) {
  printf("%d\n", i);
}

The output would be:

0
1
2
3

While Loop

The while loop creates a loop that is executed as long as a specified condition evaluates to true. The loop will continue to run until the condition evaluates to false. The condition is specified before the loop, and usually, some variable is incremented or altered in the while loop body to determine when the loop should stop.

while (condition) {
  // Code block to be executed
}

For example:

int i = 0;

while (i < 5) {
  printf("%d\n", i);
  i++;
}

The output would be:

0
1
2
3
4

Do…While Loop

A do…while statement creates a loop that executes a block of code once, checks if a condition is true, and then repeats the loop as long as the condition remains true. They are used when the loop body needs to be executed at least once. The loop ends when the condition evaluates to false.

do {
  // Code to be executed at least once
} while (condition);

For example:

int x = 0;
int i = 0;

do {
  x = x + i;
  printf("%d\n", x);
  i++;
} while (i < 5);

The output would be:

0
1
3
6
10

Nested For Loop

A nested for loop is when a for loop runs inside another for loop.

The inner loop will run all its iterations for each iteration of the outer loop.

For example:

for (int outer = 0; outer < 2; outer++) {
  for (int inner = 0; inner < 3; inner++) {
    printf("%d-%d\n", outer, inner);
  }
}

The output would be:

0-0
0-1
0-2
1-0
1-1
1-2