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w1_loops.md

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C - Loops

Loops allow your programs to execute lines of code repeatedly, saving you from needing to copy and paste or otherwise repeat lines of code.

C provides a few different ways to implement loops in your program.

Infinite Loops

In an infinite loop, the lines of code between the curly braces will execute repeatedly from top-to-bottom, until and unless we break out of it (as with a break; statement) or otherwise will our program Ctrl + c.

While Loop

Useful when we want the loop to repeat an unknown number of times, and possibly not at all.

while (true)
{

}
while (boolean-expression)
{

}
  • If the boolean-expr evaluates to true, all lines of code between the curly braces will execute repeatedly, in order from top-to-bottom, until boolean-expression evaluates to false.

Do-While Loop

Useful when we want a loop to repeat an unknown number of times, but at least once.

do
{

}
while (boolean-expression)
  • This loop will execute all lines of code between the curly braces once, and then, if the boolean-expr evaluates to true, will go back and repeat that process until boolean-expr evaluates to false.

do-while loops are guaranteed to run at least one time.



For Loops

For loops are used to repeat the body of a loop a specified number of times, in this example 10.

Useful when we want a loop to repeat a discrete number of times, though you may not know the number at the moment the program is compiled.

for (int i = 0; i < 10; i++)
{

}

The process undertaken in a for loop:

  • The counter variable(s) is set int i = 0
  • The Boolean expression is checked i < 10
    • If it evaluates to true, the body of the loop executes.
    • If it evaluates to false, the body of the loop does not execute.
  • The counter variable is incremented i++ and then the Boolean expression is checked again.
for (initialization; condition; update)
{
    // code to repeat
}
  • The statement(s) in initialization are executed
  • The condition is checked
    • If true, the body of the loop executes
    • If false, the body of the loop does not execute
  • The statement(s) in update are executed, and then the condition is checked again, etc.