Why range error & how to fix it in this program?

Hi,

I can't figure out why it gives the warning "range error". The program doesn't run... Could you please give a hint for fixing it? Thanks a lot...

Code:

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// Exercise 8.5
#include "std_lib_facilities.h"
/*
write a function to reverse the order of elements in a vector
for example
        1 2 3 4 5 6
becomes
        6 5 4 3 2 1

*/

void v_rev1(vector<double>&);
void print(vector<double>&);

int main()
try {
        cout << "Enter some numbers: ";
        vector<double> v;
        double x;
        while (cin >> x)
                v.push_back(x);
       
        cout << "In reversed sequence: " << '\n';
        cout << "{";
        v_rev1(v);
        print(v);
        cout << "}" << '\n';
       
}

catch (runtime_error e) {
        cout << e.what();
}


void v_rev1(vector<double>& v1)
{
        vector<double> v2;
        for (unsigned int i = v1.size() - 1; i >= 0; --i) {
                v2.push_back(v1[i]);
        }
        v1 = v2;       
       
}

void print(vector<double>& v)
{
        for (unsigned int j = 0; j < v.size(); ++j) {
                cout << v[j];
                if (j != v.size() - 1)
                        cout << ", ";
        }
}

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I don't see any "error range" in the code you posted. Perhaps you forgot to post the error message?

Quote:

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Originally Posted by Dino

I don't see any "error range" in the code you posted. Perhaps you forgot to post the error message?

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Hi,

The warning I received is as follows:

Code:

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terminate called after throwing an instance of 'Range_error'
  what():  Range error: -1
{Abort trap

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Quote:

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Originally Posted by pantera

Hi,

I can't figure out why it gives the warning "range error". The program doesn't run... Could you please give a hint for fixing it? Thanks a lot...

Code:

---

void v_rev1(vector<double>& v1)
{
        vector<double> v2;
        for (unsigned int i = v1.size() - 1; i >= 0; --i) {
                v2.push_back(v1[i]);
        }
        v1 = v2;       
       
}

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This function, you have i as unsigned, when you reach zero, then decrement it, you're not going to be below zero as you seem to expect(Assuming unsigned int is 32 bit, you end up with the value 2^32-1 ). To solve this you could either:

A: Change the type of i to signed int.
B: Change the method to work with unsigned int.

For example you could accomplish B by doing:

Code:

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for (unsigned int i = 0; i < v1.size(); ++i) {
        v2.push_back(v1[v1.size()-1-i]);
}

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Quote:

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Originally Posted by JacobN

This function, you have i as unsigned, when you reach zero, then decrement it, you're not going to be below zero as you seem to expect(Assuming unsigned int is 32 bit, you end up with the value 2^32-1 ). To solve this you could either:

A: Change the type of i to signed int.
B: Change the method to work with unsigned int.

For example you could accomplish B by doing:

Code:

---

for (unsigned int i = 0; i < v1.size(); ++i) {
        v2.push_back(v1[v1.size()-1-i]);
}

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Hi JacobN, thanks so much for helping. It runs properly now...

Since all v_rev1() is trying to do is reverse the order of elements in the vector, why not use std::reverse() from the <algorithm> standard header?