do-while Loop

A do-while loop is like a while loop, but the condition is checked after the body runs. This guarantees the body executes at least once, even if the condition is false from the start.

Basic Syntax

do {
    // body, runs at least once
} while (condition);

int x = 5;
do {
    print(x);
    x = x + 1;
} while (x < 0);
// Output: 5

Notice: x starts at 5, and the condition x < 0 is false. But the body ran anyway, 5 was printed, because the check happens at the end.

When Would You Use This?

do-while is useful when you need to do something before deciding whether to continue. For example: asking for input, processing one item, then checking if there is more.

// Process at least one item, then check if more remain
int i = 0;
do {
    print(arr[i]);
    i = i + 1;
} while (i < 5);

Comparison: while vs do-while

Situation	while	do-while
Condition false from start	Body never runs	Body runs once
Condition checked	Before body	After body
Guaranteed execution	No	Yes, at least one iteration

int x = 10;

while (x < 5) {       // condition is false → body never runs
    print("while");
}

do {
    print("do-while");  // runs once despite x < 5 being false
} while (x < 5);

// Output: "do-while"

break and continue

break (exit immediately)

int i = 0;
do {
    if (i == 3) { break; }
    print(i);
    i = i + 1;
} while (i < 10);
// Output: 0 1 2

continue (skip to condition check)

continue jumps to the condition check at the end:

int i = 0;
do {
    i = i + 1;
    if (i == 3) { continue; }
    print(i);
} while (i < 5);
// Output: 1 2 4 5

Truthy Conditions

saQut uses C-style truthiness: 0 is false, any non-zero value is true.

int x = 5;
do {
    x = 0;
} while (x);           // x is 0 → condition is false → loop ends

Real-World Example: Input Validation

int value;
int attempts = 0;
do {
    // Simulate reading a value
    value = readInput();
    attempts = attempts + 1;
    if (attempts >= 3) { break; }
} while (value < 0);

Advanced: process-then-check

The guaranteed first run makes do-while the natural fit whenever the first item must be handled before you can know if there’s a second, including edge values like 0. Printing a number’s digits is a classic case: even 0 has one digit, and only do-while guarantees it prints:

int n = 0;
do {
    print(n % 10);      // last digit
    n = n / 10;
} while (n > 0);
// Output: 0   (a plain 'while (n > 0)' would print nothing)

With a while loop you’d have to duplicate the body once before the loop to cover the zero case; do-while expresses “do it, then decide” directly.

What’s Next?

• Organize code with functions
• Group data with structs