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

Chapter 5 ■ Programs with Repetition Logic
This means that before the computer gets to the for statement, n must have been assigned
some value and it is this value which determines how many times the loop is executed. If a value
has not been assigned to n, the for statement would not make sense and the program will crash
(or, at best, give some nonsensical output).
To illustrate, we can modify Program P5.11 to ask the user how many lines she wants to print.
The number entered is then used to control how many times the loop is executed and, hence,
how many lines are printed.
The changes are shown in Program P5.12.
Program P5.12
#include <stdio.h>
int main() {
int n;
printf("How many lines to print? ");
scanf("%d", &n);
printf("\n"); //print a blank line
for (int h = 1; h <= n; h++)
printf("%d. I must not sleep in class\n", h);
}
A sample run is shown below. We will show shortly how to neaten the output.
How many lines to print? 12
1. I must not sleep in class
2. I must not sleep in class
3. I must not sleep in class
4. I must not sleep in class
5. I must not sleep in class
6. I must not sleep in class
7. I must not sleep in class
8. I must not sleep in class
9. I must not sleep in class
10. I must not sleep in class
11. I must not sleep in class
12. I must not sleep in class
Note that we do not (and cannot) know beforehand what number the user will type. However,
that is not a problem. We simply store the number in a variable (n is used) and use n as the “final
value” in the for statement. Thus, the number the user types will determine how many times the
body is executed.
Now the user can change the number of lines printed simply by entering the desired value
in response to the prompt. No change is needed in the program. Program P5.12 is much more
flexible than P5.11.
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