General Conditional loops:

Loop that repeats while the loop control variable is > 0

Assume we use a certain amount of heating oil each week 
(a diminishing resource), and we want to display the 
amount left after each week.

printf(“Enter starting amount of oil:”);
scanf(“%lf”, &supply);
while (supply > 0)
{
	printf(“Enter gallons used:”);
	scanf(“%lf”, &used);
	supply -= used;
	if (supply > 0)
		printf(“Amount left is %f\n”, supply);
	else
		printf(“No oil left\n”);
}

sample run:
Enter starting amount of oil: 1000
Enter gallons used: 90
Amount left is 910
Enter gallons used: 60
Amount left is 850
…
Amount left is 50
Enter gallons use: 50
Amount left is 

Modify loop to print out week # and amount of oil left after 
each week. Note that week is a counter but is not a loop 
control variable.

week = 0;
printf(“Enter starting amount of oil:”);
scanf(“%lf”, &supply);
while (supply > 0)
{
	week++;
	printf(“Enter gallons used in week %d:”, week);
	scanf(“%lf”, &used);
	supply -= used;
	if (supply > 0)
		printf(“Supply at end of week %d is %f\n”, 
week, supply);
	else
		printf(“No oil left at end of week %d\n”, week);
}

sample run:
Enter starting amount of oil: 1000
Enter gallons used in week 1: 90
Supply at end of week 1 is 910
Enter gallons used in week 2: 60
Supply at end of week 2 is 850
…
Supply at end of week 19 is 50
Enter gallons used in week 20: 50
No oil left at end of week 20

Let’s change loop so we stop when we run out of oil or we 
stop after week N (a prior data item or constant).

week = 0;
printf(“Enter starting amount of oil:”);
scanf(“%lf”, &supply);
while (supply > 0 && week < N)
{
	week++;
	printf(“Enter gallons used in week %d:”, week);
	scanf(“%lf”, &used);
	supply -= used;
	if (supply > 0)
		printf(“Supply at end of week %d is %f\n”, 
                        week, supply);
	else
		printf(“No oil left at end of week %d\n”, week);
}

sample run:
Enter starting amount of oil: 1000
Enter gallons used in week 1: 90
Supply at end of week 1 is 910
Enter gallons used in week 2: 60
Supply at end of week 2 is 850
…
Supply at end of week 9 is 550
Enter gallons used in week 10: 50
Supply at end of week 10 is 500


do while loop:

Loop that always executes at least once. Loop repetition 
condition is tested after each repetition. Loop body repeats 
if the repetition conditon is true; loop exit occurs if the 
repetition condition is false. 

Example: keep reading character data until character * is 
read.

#include <stdio.h>
#define TERMINATOR '*'
int main()
{

  char next;

  do
  {
     printf("Next character or %c:", TERMINATOR);
     scanf(" %c", &next);
  } while (next != TERMINATOR);

  return 0;
}

Unlike a sentinel controlled loop – this one processes the 
terminator character (‘*’) like any other.


Sample output:
Next character or *: x
Next character or *: y
Next character or *: z
Next character or *: *

Reason for space in “ %c” – means skip white space (blank 
or return character). Otherwise, return after x would be 
treated as 2nd data character, return after y would be treated 
as 4th data character, and so on.

Function get_integer keeps reading numbers until a number 
between min and max (function arguments) is read. Value 
of min should be <= value of max.

int get_integer(int min, int max)
{
	int next_int;

	do
	{
		printf(“Enter a number between %d and %d:”,
				min, max);
		scanf(“%d”, &next_int);
	} while (next_int < min || next_int > max);

	return next_int;
}

Sample call:  

num = get_int(1, 10);  /*num set to value from 1 thru 10*/


volts = get_int(5, 15); /* volts set to value from 5 thru 15 */

 

Function get_digit keeps reading characters until first digit 
character is read. Returns first digit character as its “result”. 
Note: digit characters form a sequence: ‘0’, ‘1’, … ‘9’

char get_digit()
{
	char next;

do
{
		printf(“Enter a digit:”);
		scanf(“ %c”, &next);
	} while (next < ‘0’ || next > ‘9’);

	return next;
}

Sample call:  
next_ch = get_digit();

What does this function do?

char mystery_1()
{
	char next;

do
{
		printf(“Enter a character:”);
		scanf(“ %c”, &next);
	} while (next < ‘A’ || next > ‘Z’);

	return next;
}

Sample call:

ch = mystery_1();

What does this function do?

char mystery_1()
{

	char next;

        do
        {
		printf(“Enter a character:”);
		scanf(“ %c”, &next);
	} while (next < ‘a’ || next > ‘z’);

	return next;
}

Sample call:

ch = mystery_2();