CODEWITHSUNDEEP
c++multiplication
baskoala
baskoala

Reputation: 11

Why there is wrong result for a simple C++ program? Is it caused by #define?

Can I know what is the reason for the output of t_temp is 1.47123e+9 rather than 3.1536e+10 (t)?

The codes of program is: 

#include<iostream>
using namespace std;
#define asd 86400    

int main()
{
    double t, t_temp;    

    t = 31536000000;
    t_temp = 365000 * asd;

    cout << t << endl;
    cout << t_temp << endl;    

    return 0;
}

Upvotes: 0

Views: 126

Answers (2)

MSalters
MSalters

Reputation: 179930

In a sense, YES, this is caused by #define.

The following 2 changes also fixes the problem (pick one)

const long long asd = 86400;

const double asd = 86400;

Upvotes: 0

Alexey Usachov
Alexey Usachov

Reputation: 1374

When you calculate expression with integer values it casts to int32_t type, and the result is more than 2^32. You need to cast at least one of the operand to higher type.

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

#define asd 86400

int main()
{
    cout << std::numeric_limits<int32_t>::max()<<endl;//2147483647
    int16_t Int16Res = 365000 * asd;//Int16Res    int16_t    11264
    int32_t Int32Res = 365000 * asd;//Int32Res    int32_t    1471228928
    int64_t Int64Res1 = 365000 * asd; //Int64Res1    int64_t    1471228928
    int64_t Int64Res2 = uint64_t(365000) * asd; //Int64Res2    int64_t    31536000000

    double t, t_temp;
    t = 31536000000;
    t_temp = 365000.0 * asd;//t_temp    double    31536001024
    cout << t_temp << endl;
    return 0;
}

Upvotes: 1

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