Casio Z-1

98
Nested loops
The term nested loop means simply “loops inside of loops”. To better understand
how nested loops work, let’s have a look at a very short, simple representative
program.
/* nested loops example */
/* #include <stdio.h> */
main(){
float a[3][3];
int i,j;
for (i=0; i<3; i++)
for (j=0; j<3; j++)
scanf(“%f”,&a[i][j]);
}
The program uses a pair of “for” loops to read values from the keyboard and assign
them to a 3x3 2-dimensional array a[3][3]. Remember that such an array looks
something like the following:
a[0][0] a[0][1] a[0][2]
a[1][0] a[1][1] a[1][2]
a[2][0] a[2][1] a[2][2]
Considering just the loop counter (i and j) values, the above program executes as
follows:
First pass (i)
Second pass (i)
Third pass (i)
i=0
j=0
j=1
j=2
i=1
j=0
j=1
j=2
i=2
j=0
j=1
j=2
This means that values entered from the keyboard are read into “%f” by scanf() and
assigned to array a[3][3] in sequence by “&a[i][j] as “i” and “j” change values as noted
above.
Let’s expand on this program so that a second nested loop reads the values out of
the array and displays them on the screen.
/* nested loops example 2 */
/* #include <stdio.h> */
main(){
float a[3][3];
int i,j;
for (i=0; i<3; i++)
for (j=0; j<3; j++)
scanf(“%f”,&a[i][j]);
for (i=0; i<3; i++) {
for (j=0; j<3; j++)
printf(“%8.2f”,a[i][j]);
printf(“¥n”);
}
}