Pre Increment Operators

C - Difference between ++i and i++:

C offers several shorthand versions of the preceding type of assignment. When the operators precede (i.e., come before) the variable, the operation is called pre-increment and when the operators succeed (i.e., come after) the variable, the operations is called post-increment. Consider the following code snippets:

total = i++;    /* Statement 1 */
and 
total = ++i;    /* Statement 2 */

The first statement is equivalent to:

total = i;
i = i + 1;

while the second statement is equivalent to:

i = i + 1;
total = i;

So, the said statements (1) and (2) do not have the same effect. The ++ in i++ is called post increment operator and ++i is called the pre increment operator.

Example: ++i and i++

#include <stdio.h>

int main() 
{
 int total = 100;
 int i = 10;
 printf("The initial value of total and i is : %d, %d", total, i);
 total = ++i;
 printf("\nAfter applying ++i value of total and i is : %d, %d", total, i);
 total = 100;
 i = 10;
 printf("\n\nThe initial value of total and i is : %d, %d", total, i);
 total = i++;
 printf("\nAfter applying i++ value of total and i is : %d, %d", total, i);
 return 0;
}

Output:

The initial value of total and i is : 100, 10
After applying ++i value of total and i is : 11, 11

The initial value of total and i is : 100, 10
After applying i++ value of total and i is : 10, 11

++ in for construct:

In the following for construct:

for (i =0; i++<5;..)

The value of i is compared 5 and then incremented, after which the loop is entered.
On the other hand, if the construct is modified to:

for (i=0; ++ i < 5;..)

The value of i is first incremented and then compared to 5 and then the loop is entered.
So in the first case the body of the loop will be executed 5 times and in the second case it will be executed 4 times only.

Example: i++ in for construct:

#include <stdio.h>
int main() 
{
	printf("i++ in for construct:");
	for (int i =0; i++<5;)
	{
		printf("\nValue of i is %d",i);
	}
 return 0;
}

Output:

i++ in for construct:
Value of i is 1
Value of i is 2
Value of i is 3
Value of i is 4
Value of i is 5

Example: ++i in for construct:

#include <stdio.h>
int main() 
{
	printf("++i in for construct:");
	for (int i =0; ++i<5;)
	{
		printf("\nValue of i is %d",i);
	}
 return 0;
}

Output:

++i in for construct:
Value of i is 1
Value of i is 2
Value of i is 3
Value of i is 4