const float theta_spacing = 0.07;
const float phi_spacing   = 0.02;

const float R1 = 1;
const float R2 = 2;
const float K2 = 5;
// Calculate K1 based on screen size: the maximum x-distance occurs
// roughly at the edge of the torus, which is at x=R1+R2, z=0.  we
// want that to be displaced 3/8ths of the width of the screen, which
// is 3/4th of the way from the center to the side of the screen.
// screen_width*3/8 = K1*(R1+R2)/(K2+0)
// screen_width*K2*3/(8*(R1+R2)) = K1
const float K1 = screen_width*K2*3/(8*(R1+R2));

render_frame(float A, float B) {
  // precompute sines and cosines of A and B
  float cosA = cos(A), sinA = sin(A);
  float cosB = cos(B), sinB = sin(B);

  char output[0..screen_width, 0..screen_height] = ' ';
  float zbuffer[0..screen_width, 0..screen_height] = 0;

  // theta goes around the cross-sectional circle of a torus
  for (float theta=0; theta < 2*pi; theta += theta_spacing) {
    // precompute sines and cosines of theta
    float costheta = cos(theta), sintheta = sin(theta);

    // phi goes around the center of revolution of a torus
    for(float phi=0; phi < 2*pi; phi += phi_spacing) {
      // precompute sines and cosines of phi
      float cosphi = cos(phi), sinphi = sin(phi);
    
      // the x,y coordinate of the circle, before revolving (factored
      // out of the above equations)
      float circlex = R2 + R1*costheta;
      float circley = R1*sintheta;

      // final 3D (x,y,z) coordinate after rotations, directly from
      // our math above
      float x = circlex*(cosB*cosphi + sinA*sinB*sinphi)
        - circley*cosA*sinB; 
      float y = circlex*(sinB*cosphi - sinA*cosB*sinphi)
        + circley*cosA*cosB;
      float z = K2 + cosA*circlex*sinphi + circley*sinA;
      float ooz = 1/z;  // "one over z"
      
      // x and y projection.  note that y is negated here, because y
      // goes up in 3D space but down on 2D displays.
      int xp = (int) (screen_width/2 + K1*ooz*x);
      int yp = (int) (screen_height/2 - K1*ooz*y);
      
      // calculate luminance.  ugly, but correct.
      float L = cosphi*costheta*sinB - cosA*costheta*sinphi -
        sinA*sintheta + cosB*(cosA*sintheta - costheta*sinA*sinphi);
      // L ranges from -sqrt(2) to +sqrt(2).  If it's < 0, the surface
      // is pointing away from us, so we won't bother trying to plot it.
      if (L > 0) {
        // test against the z-buffer.  larger 1/z means the pixel is
        // closer to the viewer than what's already plotted.
        if(ooz > zbuffer[xp,yp]) {
          zbuffer[xp, yp] = ooz;
          int luminance_index = L*8;
          // luminance_index is now in the range 0..11 (8*sqrt(2) = 11.3)
          // now we lookup the character corresponding to the
          // luminance and plot it in our output:
          output[xp, yp] = ".,-~:;=!*#$@"[luminance_index];
        }
      }
    }
  }

  // now, dump output[] to the screen.
  // bring cursor to "home" location, in just about any currently-used
  // terminal emulation mode
  printf("\x1b[H");
  for (int j = 0; j < screen_height; j++) {
    for (int i = 0; i < screen_width; i++) {
      putchar(output[i,j]);
    }
    putchar('\n');
  }
  
} 

C Language online compiler

Write, Run & Share C Language code online using OneCompiler's C online compiler for free. It's one of the robust, feature-rich online compilers for C language, running the latest C version which is C18. Getting started with the OneCompiler's C editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose language as 'C' and start coding!

Read inputs from stdin

OneCompiler's C online editor supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample C program which takes name as input and print your name with hello.

#include <stdio.h>
int main()
{
    char name[50];
    printf("Enter name:");
    scanf("%s", name);
    printf("Hello %s \n" , name );
    return 0;
    
}

About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
} 

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
} 

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}  

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition); 

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}