What are the three loop constructs in C?

while tests before the body (0+ runs), do-while tests after (1+ runs), and for bundles init/test/update for counted loops.

* while tests before the body (0+ runs), do-while tests after (1+ runs), and for bundles init/test/update for counted loops. *

while - check THEN execute (0 or more iterations):

while (condition) {
    statement;
}

// Example:
while (a && *a) {
    c += *a;
}

do-while - execute THEN check (1 or more iterations):

do {
    statement;
// Note the semicolon!
} while (condition);

// Example: Always runs at least once
do {
    c += *a;
} while (a && *a);

for - init; test; update:

for (init; condition; update) {
    statement;
}

// Example:
for (i = 0; i < N; i++) {
    c += a;
}

// Multiple variables:
for (i = 0, c = 7; i < N; i++, c--) {
    c += a;
}

Tip: Use for when you know the iteration count, while when you don't, do-while when you need at least one iteration.