Iterative Programming is executing a specific code block several time until an exit condition is met.
There are four ways to do Iterative Programming in C#
- for Loops
- foreach loop
- while loop
- do while loop
For Loop
Syntax
for(variable initialization; condition ; variable increment) {
//code block goes here
}
Example:
for( int i=0;i<10;i++) {
Console.Write(i);
}
Output: 12345678910
Explanation:
We want to execute the body of the loop as long as an integer i < 10 starting from i=0 and incrementing it by 1 in each iteration.
Example:
for (char c = 'a'; c < ='z'; c++) {
Console.Write(c);
}
Output: abcdefghijklmnopqrstuvwxyz
Explanation:
We want to execute the body of the loop as long as a character c < ‘z’ starting from a and incrementing it by one letter in each iteration.
Loops are very effective in working hand to hand with arrays specially when we want to navigate through array items.
Example: The follwoing program displays only even number from the given array list of integers.
int [] nums = {1,2,3,4,5,6,7,8,9,10};
for( int i=0;i<10;i++) {
if(nums[i] %2 == 0)
Console.Write(nums[i]);
}
Output: 1235678910
Foreach loop
Foreach loop is similar to for loop but it is a has a relatively shorter syntax. Basically it iterates over a collection of list items and do something with the items while a for loop uses index based access system which works based with index based collections like arrays.
Example:
int[] nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
foreach (int digit in nums) {
if (digit % 2 == 0)
Console.Write(digit);
}
Example:
List<int> digits = new List<int> { 1, 2, 3, 4, 5, 6, 7, 8, 9,10 };
foreach(int digit in digits ) {
if(digit %2 == 0)
Console.Write(digit);
}
Output: 2 4 6 8 10
While loop
while loop is a litter different than for loop, we do the initialization part outside of the while loop and the increment part in side the code block
Syntax:
variable initialization
while(condition ) {
//code block goes here
variable increment
}
Example:
int i=0;
while( i<10) {
Console.Write(i);
i++;
}
char c = 'a';
for ( c < ='z';) {
Console.Write(c);
c++;
}
While loop are used when you don't know how many times you want to loop through the code block and you just want to execute it until some condition is met which is triggered by what is going on in side the code block.
do while loop
do while loop is a kind of the same as while loop, we do the initialization part outside of the while loop and the increment part in side the code block but it is is different due to small syntax difference.
Syntax:
variable initialization
do{
//code block goes here
variable increment
} while(condition) ;
Example:
int i=0;
do {
Console.Write(i);
i++;
} while( i<10) ;
Output 0123456789
As you can see, the code block always is executed at least once regardless of the condition set in the while statement.
Nested Loops
Nested loops are loops that are inside other loop. We call the outside loop outer loop and the inside one inner loop.
We can use any of the above loop type (for, while, do.. while) to create a nested loop.
The time complexity of nested loops(how many times the body of the inner loop shall be executed) can be calculated using N time M, where N is the size of the outer loop and M is the size of the inner loop.
Nester loop are perfect fit for navigating a multi-dimensional arrays.
Let's see an example:
We want to represent the following table in a two dimensional array and retrieve it back.
int[,] array = new int[3, 4];
array[0, 0] = 1;
array[0, 1] = 10;
array[0, 2] = 5;
array[0, 3] = 9;
array[1, 0] = 5;
array[1, 1] = 2;
array[1, 2] = 3;
array[1, 3] = 4;
array[2, 0] = 6;
array[2, 1] = 8;
array[2, 2] = 5;
array[2, 3] = 5;
for (int i=0; i<array.GetLength(0); i++) {
for(int j=0; j< array.GetLength(1); j++) {
Console.Write(array[i, j] + " " );
}
Console.WriteLine();
}