Thread: confused about 'for'

Confused about output of following 2 sets of code. Postfix and Prefix notation.

the way I understood book:

Using Xcode 3.3 , gcc 4.2


postfix notation passes on value to i before it increments.

prefix notation increments before it passes value to i.
-----------------------------------------------------------
Postfix notation code
-----------------------------------------------------------
for (i = 0; i < 4; i++)

printf( "first for: i=%d\n", i );

printf( "After first for loop, i=%d.\n\n", i );
------------------------------------------------------------
Postfix notation code output
------------------------------------------------------------
first for: i=0
first for: i=1
first for: i=2
first for: i=3
After first for loop, i=4.
-------------------------------------------------------------
Prefix notation code
-------------------------------------------------------------
for (i = 0; i < 4; ++i)

printf( "first for: i=%d\n", i );

printf( "After first for loop, i=%d.\n\n", i );
-------------------------------------------------------------
Prefix notation code output
-------------------------------------------------------------
first for: i=0
first for: i=1
first for: i=2
first for: i=3
After first for loop, i=4.

Why do both sets of code output the same?

rj

Here is another way of thinking about how your for loop works:

Code:

    i = 0;
    while (i < 5) {
        printf("%d\n", i);
        i++;
    }

Can you see why it would make no difference at all in your code as to whether you use pre or post increment?

Anyway, if you want to compare the results you were getting with something more like you wanted, look at this code:

Code:

#include <stdio.h>

int main(void)
{
    int i;
    int x = 0;
    int y = 0;

    puts("");

    for (i = 0; i < 5; i++) {
        printf("%d\n", i);
    }

    puts("");

    for (i = 0; i < 5; ++i) {
        printf("%d\n", i);
    }


    puts("");

    for (i = 0; i < 5; i++) {
        printf("x = %d\ty = %d\n", x++, ++y);
    }

    puts("");

    return 0;
}