Need help with this little C program

User 11946215

Hey guys, I have to write a small program in C, I'll explain what it has to do. You have product a, b and c The input is the prices of a, b and c in cents. You have to spend exactly 100 euros on the purchase of exactly 100 products. As output I need to get a list of all possible combinations. Lets give an example. Lets say the input is "88 99 102": then the output has to be exactly like this: 1 a, 62 b, 37 c 4 a, 48 b, 48 c 7 a, 34 b, 59 c 10 a, 20 b, 70 c 13 a, 6 b, 81 c I'm relatively new in progamming in C, so all help is appreciated, the deadline is short for this one.

int main(int argc, char *argv[]) {
int a, b, c, x, y, z /* x=numbers of a y= numbers of b z= numbers of c*/
printf("price of a:\n");
printf("price of b:\n");
printf("price of c:\n");
scanf("%d, %d, %d" ,&a, &b, &c);
while (x+y+z=100){
x*a+y*b+z*c=10000

As you can see, I tried writing some code, but im stuck right here...

Lost User

This is not a programming problem, more one of mathematics. You first need to work out the algorithm to calculate the numbers of each product that you can buy for €100. Once you have that then turning it into code should be fairly trivial.

CPallini

A brute force approach would work, e.g.

for ( x = 1; x <= 98; x++)
for ( y = 1; y <= (99 - x); ++y)
{
z = 100 - x - y;
// here check if the items sum to 100
}

User 11946215

Thanks. I'm finally getting the hang of it. I'll try something tomorrow and I will let you peoples know if I succeed or not.

User 11946215

Thank you guys. I can't compile and execute right now. Will this give me the output I want? If not, where did I go wrong?

#include #include #include int main(int argc, char *argv[])
{
int a, b, c, x, y, z; /* x=numbers of a y= numbers of b z= numbers of c*/
printf("price of a:\n");
printf("price of b:\n");
printf("price of c:\n");
scanf("%d, %d, %d" ,&a, &b, &c);

for(x = 1; x <= 100; x++)
{
	for(y = 1; y <= (100 - x); ++y)
	{
		z = 100 - x - y;
		if(x\*a + y\*b + z\*c == 100)
		{
    		printf("x %d, y %d, z %d",a ,b ,c);
		}
	}
}

return 0;
}

CPallini

You are welcome.

User 11946215

Thanks again, I make improve in the code, but it ain't working as supposed. I'm really wondering where the code is wrong, I get no output or a wrong output (e.g. 100 100 100 gives as output only 100 a, 0 b, 0 c.) I tried different things and I guess I'm almost there, but can't fix it. So please, help me with this code.

#include #include #include int main(int argc, char *argv[])
{
int a, b, c, x, y, z; /* x=numbers of a y= numbers of b z= numbers of c*/
printf("price of a:\n");
printf("price of b:\n");
printf("price of c:\n");
scanf("%d, %d, %d" ,&a, &b, &c);

for(x = 0; x <= 100; x++)
{
	for(y = 0; y <= (100 - x); ++y)
	{
		        z = 100 - x - y;
		        if(x\*a + y\*b + z\*c == 10000)
		        {
    		      printf("%d a, %d b, %d c",x ,y ,z);
		        }
	}
}

return 0;
}

CPallini

You don't use correctly scanf. Try

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(int argc, char *argv[])
{
int a, b, c, x, y, z; /* x=numbers of a y= numbers of b z= numbers of c*/

int done = 0;

while ( done == 0)
{
printf("please enter the price of a:\n");
if ( scanf("%d", &a) != 1) continue;
printf("please enter the price of b:\n");
if ( scanf("%d", &b) != 1) continue;
printf("please enter the price of c:\n");
if ( scanf("%d", &c) != 1) continue;
done = 1;
}

for(x = 0; x <= 100; x++)
{
for(y = 0; y <= (100 - x); ++y)
{
z = 100 - x - y;
if(x*a + y*b + z*c == 10000)
{
printf("%d a, %d b, %d c\n",x ,y ,z);
}
}
}

return 0;
}

User 11946215

Thank you so much! It works great. I had to change the code a bit to pass all testcases, but finally I made it :). However, I'd like to know how that piece of code between the While { ... } works, I don't really get it. done = 0, so while ( done == 0) is true. Then it runs the code and you can enter the values. But why does it need the done == 0 and why the != 1? I understand the done = 1, otherwise it will run the while statement again, right?

User 11946215

Well, I don't know why it did not work the first time, but I tried to simplify the code and ended up with: printf("price of a: price of b: price of c: "); scanf("%d %d %d", &a, &b, &c); instead of that thing with while { ... } And this time, it did work. I do not really see the difference with the code I used before that did not work.. :p

CPallini

Even the code you used before would have work with a suitable input, that is if the user would have entered, for instance

100,100,100

that is, with the commas. However, the code handling input from the user should be more robust.

David Crow

Perhaps your problem can be broken up into two smaller problems: 1) Find all combinations of A+B+C that equal (quantity) 100. I *think* that gives you a set of about 4851 combinations. 2) For each of those, multiply A by 0.88, b by 0.99, and C by 1.02, and if that product equals 100 euros, you have a match.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

User 11946215

That sounds like a faster way to calculate, because of the smaller set of combinations. I'd like to try that another time, but I don't have the time to do that now before the deadline. Thanks for the tip, nice to see how there are multiple solutions to work it out.