Excercise Solutions

Walkthroughs

Walkthrough 1:

What is the output of the following program?

#include <stdio.h>
int main(void){
	int x=1;
	int y=1;
	printf("whole thing: %d\n", x = y += 3 / 4 + 5 * 2 % 3 - 6);
	printf("x = %d, y = %d\n", x , y);
	x = 2;
	y = 2;
	printf("x++ = %d\n", x++);
	printf("++y = %d\n", y++);
	printf("x = %d\n", x);
	printf("y = %d\n", y);
	return 0;
}

Solution:

whole thing: -4
x = -4, y = -4
x++ = 2
++y = 2
x = 3
y = 3

Walkthrough 2:

What is the output of the following program?

#include <stdio.h>
int main(void){
	int x=1;
	float y=1;
	printf("whole thing: %d\n", x = y = (9 * 2.0 - 2 % 3 * 5) / 3);
	printf("x = %d, y = %f\n", x , y);
	return 0;
}

Solution:

whole thing: 2
x = 2, y = 2.666667

Debugging

Here is the original code:

#include <stdio.h>
int main(void)}
    integer x=0;
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    return 0
}

Here are the syntax errors:

1. } instead of { on the int main(void)} line
2. integer should be int in the integer x = 0; line
3. missing ; on the return 0 line

Logical errors:

x is initially 0, the first line of output outputs x++. since x++ results in the original value of x, the first output would be 0. This program prints:

0
1
2
3
4

To fix this, we can do one of two things. Either we initialize x with 1 (int x = 1) or we use prefix increment instead printf("%d\n", ++x); on each line

Thus, the solution is either:

#include <stdio.h>
int main(void)
{
    int x=1;
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    printf("%d\n",x++);
    return 0;
}

or:

#include <stdio.h>
int main(void)
{
    int x=0;
    printf("%d\n",++x);
    printf("%d\n",++x);
    printf("%d\n",++x);
    printf("%d\n",++x);
    printf("%d\n",++x);
    return 0;
}