Need Quick Help

[mmki]

This is for an equation for the time it takes a pendlum to swing

#include <iostream>
#include <cmath>
#define PI 3.14159
#define G 9.8 //Gravity

using namespace std;

int main()
{
double l;
double e;
cout << "Enter Lengh of Rod\n";
cin >> l;
cout << "The time it takes from one swing is ";
cout << 2*PI*((l/G)^(1/2));
cin >> e;
return 0;
}





i get error; invalid operands of types `double' and `int' to binary `operator^'

HELP!!
thanks

 

[Swan]

^ is a bitwise operator. It doesn't mean powers in C++.

I'd fix it for you, but I need to go to school.

You want to be using the pow() function which I believe is part of the math.h.

http://www.cplusplus.com/reference/clibrary/cmath/pow/

 

[super_]

/*
 * pendulum_time.c
 *
 * Calculates the time for a pendulum to complete one swing.
 *
 * 8/24/09 - super_
 */

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

#define PI	3.14159
#define G	9.8

main() {
    double rod_length;
    double swing_time;

    printf("Enter length of rod: ");
    scanf("%lf", &rod_length);

    swing_time = 2 * PI * sqrt(rod_length / G);

    printf("Time it takes for one swing: %f\n", swing_time);

    return 0;
}

Improved.

 

[Swan]

/*
 * pendulum_time.c
 *
 * Calculates the time for a pendulum to complete one swing.
 *
 * 8/24/09 - super_
 */

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

#define PI	3.14159
#define G	9.81

[b]int[/b] main([b]int argc, char* argv[][/b]) {
    double rod_length;
    double swing_time;

    printf("Enter length of rod: ");
    scanf("%lf", &rod_length);

    swing_time = 2 * PI * sqrt(rod_length / G);

    printf("Time it takes for one swing: %f\n", swing_time);

    return 0;
}

Improved.

Improved again.
While that may be legitimate C code for some compilers, others won't like the fact that you haven't specified a data type for the main method. As for the command line arguments, it's simply good practice to place them there.

Also, I always thought that gravity was 9.81 rather than 9.8, but I suppose that won't matter too much.

 

[super_]

Improved again.
While that may be legitimate C code for some compilers, others won't like the fact that you haven't specified a data type for the main method. As for the command line arguments, it's simply good practice to place them there.

Also, I always thought that gravity was 9.81 rather than 9.8, but I suppose that won't matter too much.

It's legit for all compilers; implicit data type is int (k&r). Command line arguments aren't to be placed there; main() means 'function main with unknown arguments', not 'no arguments'. I leave it as 'unknown arguments' so that the real entry point can still push argc, argv, and envp on the stack but I don't need to access them. The stack is cleaned after main() returns anyway

 

[Swan]

It's legit for all compilers; implicit data type is int (k&r). Command line arguments aren't to be placed there; main() means 'function main with unknown arguments', not 'no arguments'. I leave it as 'unknown arguments' so that the real entry point can still push argc, argv, and envp on the stack but I don't need to access them. The stack is cleaned after main() returns anyway

What I'm saying is that you aren't exactly complying to the standard most people use, which can confuse people.

Also, many compilers will throw errors if you don't explicitly state the return type.

 

[hampe-92]

Also, I always thought that gravity was 9.81 rather than 9.8, but I suppose that won't matter too much.

pretty much of topic but, what gravity is equal to differs depending on where on the earth you are (e.g. in Sweden we use g &#8776; 9.82)...

 

[mmki]

Thanks Tons Guys =)

 

[clint999]

It's legit for all compilers; implicit data type is int (k&r). Command line arguments aren't to be placed there; main() means 'function main with unknown arguments', not 'no arguments'. I leave it as 'unknown arguments' so that the real entry point can still push argc, argv, and envp on the stack but I don't need to access them. The stack is cleaned after main() returns anyway

 

[super_]

It's legit for all compilers; implicit data type is int (k&r). Command line arguments aren't to be placed there; main() means 'function main with unknown arguments', not 'no arguments'. I leave it as 'unknown arguments' so that the real entry point can still push argc, argv, and envp on the stack but I don't need to access them. The stack is cleaned after main() returns anyway

what is your purpose?