Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 5 ■ Programs with Repetition Logic
A look at the output reveals that each line consists of three parts:
1. A number on the left that increases by 1 for each new line.
2. A fixed part " x 2 = " (note the spaces) that is the same for each line.
3. A number on the right; this is derived by multiplying the number on the
left by 2.
We can produce the numbers on the left by using this statement:
for (int m = 1; m <= 12; m++)
We then print m each time through the loop. And we can produce the number on the right by
multiplying m by 2.
Program P5.13 shows how to write it. When run, it will produce the table above.
Program P5.13
#include <stdio.h>
int main() {
for (int m = 1; m <= 12; m++)
printf("%2d x 2 = %2d\n", m, m * 2);
}
Note the use of the field width 2 (in %2d) for printing m and m * 2. This is to ensure that the
numbers line up as shown in the output. Without the field width, the table would not look neat—
try it and see.
What if we want to print a “7 times” table? What changes would be needed? We would just
need to change the printf statement to
printf("%2d x 7 = %2d\n", m, m * 7);
Similarly, if we want a “9 times” table, we would have to change the 7s to 9s. And we would
have to keep changing the program for each table that we want.
A better approach is to let the user tell the computer which table he wants. The program will
then use this information to produce the table requested. Now when the program is run, it will
prompt:
Enter type of table:
If the user wants a “7 times” table, he will enter 7. The program will then go ahead and
produce a “7 times” table. Program P5.14 shows how.
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