Writing loops within loops
There's a number of occassions when we wish to loop a number of times
(and so we use a for loop)
and within that loop we wish to perform another loop.
While a little confusing,
this construct is often quite common.
It is termed a nested loop.
#define NROWS 6
#define NCOLS 4
for(int row = 1 ; row <= NROWS ; row = row+1) { // the 'outer' loop
for(int col = 1 ; col <= NCOLS ; col = col+1) { // the 'inner' loop
printf("(%i,%i) ", row, col); // print row and col as if "coordinates"
}
printf("\n"); // finish printing on this line
}
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The resulting output will be:
(1,1) (1,2) (1,3) (1,4)
(2,1) (2,2) (2,3) (2,4)
(3,1) (3,2) (3,3) (3,4)
(4,1) (4,2) (4,3) (4,4)
(5,1) (5,2) (5,3) (5,4)
(6,1) (6,2) (6,3) (6,4)
Notice that we have two distinct loop-control variables,
row and col.
Each time that the inner loop (col's loop) starts,
col's value is initialized to 1,
and advances to 4 (NCOLS).
As programs become more complex,
we will see the need for, and write, all combinations of:
- for loops within for loops,
- while loops within while loops,
- for loops within while loops,
- and so on....
CITS2002 Systems Programming, Lecture 2, p14, 26th July 2022.
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CITS2002