C: Loops for data pairs using while

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C: Loops for input

There are times when adjacent pairs of data need to be considered or processed together. Consider the following sequence of integers.

8 6 4 10 5 2 Here is a sequence of lines highlighting each of the pairs.

8 6

6 4

4 10

10 5

5 2

The code below shows how to read in a series of integers and then add adjacent pairs together.

Note that a trailer loop is used where a negative value terminates the pairs. A variable is used to remember the last value so that adjacent pairs can be processed. Here is the C code.

#include <stdio.h>

int main() {
	int leftValue1;
	int rightValue1;
	int dataPos1;
	int pairPos1;
	scanf("%d",&rightValue1);
	dataPos1 = 0;
	pairPos1 = 0;
	while (rightValue1 >= 0) {
		dataPos1 += 1;
		printf("\n");
		printf("Data value #%d is %d\n",dataPos1,rightValue1);
		if (dataPos1 != 1) {
			pairPos1 += 1;
			printf("Pair #%d is %d and %d.\n",pairPos1,leftValue1,rightValue1);
			}
		leftValue1 = rightValue1;
		scanf("%d",&rightValue1);
		}
	printf("\n");
	printf("Data values processed: %d\n",dataPos1);
	printf("Pairs processed: %d\n",pairPos1);
	return 0;
	}

Here are some examples of input and output for the above program code.

Here is an example input.

For the above example input, here is the expected output.

Data value #1 is 8

Data value #2 is 6
Pair #1 is 8 and 6.

Data value #3 is 4
Pair #2 is 6 and 4.

Data value #4 is 10
Pair #3 is 4 and 10.

Data value #5 is 5
Pair #4 is 10 and 5.

Data value #6 is 2
Pair #5 is 5 and 2.

Data values processed: 6
Pairs processed: 5

Here is an example input.

For the above example input, here is the expected output.

Data value #1 is 7

Data value #2 is 3
Pair #1 is 7 and 3.

Data value #3 is 5
Pair #2 is 3 and 5.

Data values processed: 3
Pairs processed: 2

Note that if you fail to read in the rightValue1 at the end of the loop body, the loop will never terminate (assuming the loop body is executed at least once).