invalid conversion from 'const char*' to 'int'

Question

2.38/5 (3 votes)

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C++

#include <iostream>
#include <string>
using namespace std;

class Mint {
public:

	Mint();
	Mint(int);
	Mint (string s);
private:
	int num[];
};
Mint::Mint()
{
	num[0] = 0;
}

Mint::Mint(int n)
{
	int i=0;
	while(n>0)
	{
		num[i] = n%10;
		n = n/10;
		i++;
	}
}
Mint::Mint(string s)
{
	int i = 0 ;
	while(s[i] != '\0')
	{
		i++;
	}
	i--;
	while(i>=0){
		num[i] = s[i] - '0';
		i--;
	}
}
int main()
{
	Mint x;
	Mint y;
	Mint z=50014;
	Mint a="065272005572"; //its important that i initialize this way  
}

when i try to compile i get an error
invalid conversion from 'const char*' to 'int' Mint a="065272005572"
and
initializing argument 1 of 'Mint::Mint(int)' [-fpermissive]
Mint(int);
any help;

Posted 26-Dec-15 2:28am

Member 12223678

Updated 21-May-23 7:12am

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Comments

[no name] 26-Dec-15 9:04am

You can use
Mint a= string("065272005572");
But this will not be the only Problem you will face. Accessing "int num[];" without "allocate" it, will be the much bigger one.... and some other ones.

Member 12223678 26-Dec-15 9:07am

thank you but is there a way that i can initialize this way
Mint = "06214589547447"

[no name] 26-Dec-15 9:10am

Why?
Yes there is, in case you Support Mint::Mint(const char* s)

Member 12223678 26-Dec-15 9:18am

can you please explain what other problems that i have

Member 12223678 26-Dec-15 9:14am

Mint::Mint(const char* s)
{
int i = 0 ;
while(s[i] != '\0')
{
i++;
}
i--;
while(i>=0){
num[i] = s[i] - '0';
i--;
}
}
something like this

[no name] 26-Dec-15 9:18am

Yes something like this (which makes btw much more sense to detect end_of_string. You used the same for string, but string class gives you smarter options).

Please take care where you write a reply. This to make sure that you reach the "original person" :-)

Member 12223678 26-Dec-15 9:26am

thnx
the compilation worked but the program doesnt run , could you please explain to me the other problems that i have in the code

[no name] 26-Dec-15 9:31am

Please explain what "doesn't run" means. And think again about "int num[];", what is the size of it?

Member 12223678 26-Dec-15 9:35am

when i specify the size like num[50] or something like that it works just fine
but is there a way to dynamically allocate memory

[no name] 26-Dec-15 9:44am

Yes there is! Google please first a bit by yourself and also think more deep about it, in the sense:
a.) What time you Need to allocate/"reallocate" and what you Need to do in case for "reallocate"
b.) What time you Need to release

Some hints, think about:

int num_VecSz;
int* num;

// Make sure to initialize num to NULL and VecSz to 0. Ok one of them is basically enough, but one of them gives you the info whether you have allocated or not.

// Allocate
num= new int[num_VecSz];

// Release
delete[] num;
num_VecSz= 0; // Sorry forgot this :(

Philippe Mori 26-Dec-15 18:10pm

If you don't know how memory works, you should first learn that. Otherwise, you will have programs that crash and corrupt memory.

Or uses containers that already manage their memory like std::vector.

Or works in another language that uses a garbage collector.

Or read books like those from Scott Meyers.

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Aescleal · Answer 1 · 2015-12-26T09:43:00

Your code's got three immediate problems.

The first one (and the one the compiler's having a whine about) is that it can't work out which constructor you want called. When you give it an int it can work out you want the first called. However when you give it a const char * it has no idea that you want the string constructor called. So if you want the string constructor called actually give it a string!

C++

Mint b{ std::string{ "1234567" } };

is the sort of thing you need to use if you've got a modern compiler

C++

Mint b( std::string( "1234567" ) );

if you haven't.

Second problem is how you're storing your digits. A better way than using a built in array is to use a std::vector. It's dynamically resizable and, once sized, is usually as fast as a built in array.

The final problem is handling copying and assignment of your objects. Consider what happens when you do things like:

Mint a = 137;<br />
Mint b = a;<br />

Hopefully if you use a vector to store your digits this problem solves itself but if you try and manage memory yourself then it's something you should consider.

Gevorg Hai · Answer 2 · 2015-12-26T04:37:00

Solution 1

C++

//#include <iostream>
//#include <string>
//using namespace std;

class Mint {
public:

	Mint();
	Mint(int);
	Mint (const char*);
	~Mint();
private:
	int* m_num;
};
Mint::Mint() 
	: m_num(NULL)
{
}

Mint::~Mint()
{
	delete[] m_num;
}

Mint::Mint(int n)
{
	m_num = new int[n];
	int i=0;
	while(n>0)
	{
		m_num[i++] = n%10;
		n = n/10;
	}
}

Mint::Mint(const char* str)
{
	int i = 0 ;
	while(str[i] != '\0')
	{
		++i;
	}
	m_num = new int[i];
	--i;
	while(i>=0){
		m_num[i] = str[i] - '0';
		--i;
	}
}

Posted 26-Dec-15 4:37am

Gevorg Hai

Comments

Aescleal 26-Dec-15 14:54pm

If you're going to program like it's 1993 you could at least make sure your code handles value semantics properly.

Philippe Mori 26-Dec-15 18:13pm

Should use std::vector instead.

If you really want to use C style arrays, then at least, you should know what is a copy constructor and why you need one.

Gevorg Hai 28-Dec-15 16:43pm

Agree about copy constructor and also assinment operator.