Language Tutorials/C/Loops

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This tutorial describes loops in C and compares them to loops in Scratch.

Loops

There are three different types of loops in C; namely for, while, and do while.

For

The for loop has three parts: the initialization statement, the continue condition, and the repeated statement. A for loop can look something like this:

# include <stdio.h>

int main() {
  for (int i = 0; i < 10; i++) {
    printf("Iteration number %d\n", i);
  }
}

That code should print out "Iteration number 0", "Iteration number 1", and so on until "Iteration number 9". This is similar to the following code in Scratch:

when gf clicked
set [i v] to (0)
repeat until <not <(i) < (10)>>
say (join [Iteration number ] (i)) for (1) seconds
change [i v] by (1)
end

While

A while loop has the following format:

while (condition) {
  // do something
}

A while loop is equivalent to the following in Scratch:

repeat until <not<condition :: grey>>
...
end

A while loop starts by checking if the condition is met. If the condition is met, the code inside the brackets is executed; once the code is done executing, the whole process repeats. If not, it skips over the loop entirely.

Endless

A while loop can be used like this, creating an endless loop:

# include <stdio.h>

int main(void) {
  while (1) {
    printf("Infinite loop\n");
  }
}

It works by always meeting the loop condition, making the while loop loop infinitely. The equivalent in Scratch is:

when gf clicked
forever
say [Infinite Loop!]

Do While

A do while loop has the following syntax:

do {
// inner code
} while (condition)

The do while loop always runs the code inside the loop once. Then, it works like a while loop. The equivalent in Scratch is:

move (10) steps
repeat until <not <condition::grey>>
move (10) steps