C ++-for循环未运行

Question

Have a very simple code that I'm building in C++. This is my first C++ code so I'm not entirely sure of syntax in some places. However, for the following code, my for loop isn't running at all! I can't see why not... Can anyone spot the problem?

#include <cstdlib>
#include <cmath>

using namespace std; 


int main () {
/*
 * Use values for wavelength (L) and wave number (k) calculated from linear 
 * dispersion program
 * 
 */


//Values to calculate
  double u;                            //Wave velocity: d*phi/dx
  double du;                  //Acceleration of wave: du/dt

  int t; 
//Temporary values for kn and L (taken from linear dispersion solution)

  float L = 88.7927;
  float kn = 0.0707624;

Note: I've left out variable declarations to save on space.

/*
 * Velocity potential = phi = ((Area * g)/omega) * ((cosh(kn * (h + z)))/sinh(kn * h))*cos(k*x - omega * t);
 * Velocity of wave, u = d(phi)/dx;
 * Acceleration of wave, du = du/dt;
 */

    for (t = 0; t == 5; t++) {
      cout << "in this loop" << endl;
      u = ((kn * A * g)/omega) * ((cosh(kn * (h + z)))/sinh(kn * h)) *  cos(omega * t);
      du = (A * g * kn) * ((cosh(kn * (h + z)))/sinh(kn * h)) * sin(omega * t); 
      cout << "u = " << u << "\tdu = " << du << endl;
    }

    cout << L << kn << endl;

return 0;

}

I've put the "in this loop" as a test and it doens't enter the loop (compiles fine)..

Thanks in advance for taking a look at this!

Answer 1

t is initialized to 0 , t == 5 will always be evaluated to be false , so your for loop will never run.

update

for (t = 0; t == 5; t++) {

to

for (t = 0; t < 5; t++) {

---

for Statement

Executes a statement repeatedly until the condition becomes false .

for ( init-expression ; cond-expression ; loop-expression )

  statement; 

Answer 2

Should be:

  for (t = 0; t < 5; t++)

The syntax of for loop in C++ is:

for ( init-expression ; cond-expression ; loop-expression ) 
statement;

The statement executes only while cond-expression is true and in your case it is never true.

Answer 3

That's simple: the condition for your for loop is t == 5 - it only loops as long as t is five, but since you set t = 0 at first, it doesn't loop even once. I think t < 5 is what you want.

Answer 4

Please look at the condition expression for for loop . Hint : You initialized t to 0.