Thread: What's wrong with this program, and how to fix it?

Hi,

When I compile this program, there's always a message on the screen as below:

"exer3.cpp: In function ‘int main()’:
exer3.cpp:13: warning: comparison between signed and unsigned integer expressions
exer3.cpp:18: warning: comparison between signed and unsigned integer expressions
exer3.cpp:22: warning: comparison between signed and unsigned integer expressions
exer3.cpp:27: warning: comparison between signed and unsigned integer expressions
exer3.cpp:35: warning: comparison between si "

Despite this, I am able to run the program and have the expected results. However, I don't know how to fix the areas of the program which the warnings point to. Could you please help? Thanks a lot!

Code:

// Exercise 3/Chapter 3: Programming: Principles and Practice using C++

#include "std_lib_facilities.h"

int main()
{
	vector <double> myvector;
	double number = 0;
	while (cin >> number)
		myvector.push_back(number);
	
	double sum = 0;
	int i;
	for (i = 0; i < myvector.size(); ++i)
		sum += myvector[i];
	
	// compute distance
	vector <double> mydistance;
	for (i = 0; i < (myvector.size()-1); ++i)
		mydistance.push_back(myvector[i+1]- myvector[i]);
	
	cout << "Numbers: " << endl;
	for (i = 0; i < myvector.size()-1; ++i) {
		cout << " " << myvector[i];
	}
	
	cout << "\nDistance: " << endl;
	for (i = 0; i < mydistance.size(); ++i) {
		cout <<" " << mydistance[i];	
	}
	
	// find min, max
	double max, min;
	max = min = myvector[0];
	cout << '\n';
	for (i = 0; i < myvector.size(); ++i) {
		if (myvector[i] > max) {
			max = myvector[i];
			cout << "Max = " << max << "\tMin = " << min << endl;
			min = max;
		}
		else if (myvector[i] < max) {
			min = myvector[i];
			cout << "Max = " << max << "\tMin = " << min << endl;
			max = min;
		}
		
	}
	
}

myvector.size() returns an unsigned integer type, while the loop counter is signed. One way to get rid of the warnings is to use an appropriate type, for example vector<double>::size_type (which is the type that size() returns in this case). Or you could just make the loop counter an unsigned int.

Thank you all so much for your time & help. I'm doing another program but get stuck... The program is about rewards for the inventor of chess-board. For 1st square, he's rewarded with 1 grain of rice, 2nd square for 2 grains, 3rd for 4 graints,... doubling grains for each of the 64 squares. The exercise asks me to identify how many squares are needed for at least 1,000 grains of rice, at least 1,000,000, and at least 1,000,000,000. I've tried writing the program for 1,000 grains. Where I got stuck is that, how can I write a program that accommodates all these tests (1,000, 1,000,000, etc...) in a single loop? I can't figure out how, and currently I'm just thinking of writing 3 loops for each of the 3 tests. Can you please suggest some hint? Thanks a lot.

Code:

// Exercise 8: a Game of Chess reward
#include "std_lib_facilities.h"

int main()
{
	const int N = 64;
	int grain, sum;
	
	sum = grain = 1;
	int i = 2;
	int n;
	while (i <= N) {
		grain *= 2;
		sum += grain;
		if (sum >= 1000) {
			n = i;
			cout << n <<" squares are needed for 1000 grains\n";
			cout <<"Sum of grains: " << sum << endl;
			break;
		}

		++i;
          }
}