#include <stdio.h>
#include <stdlib.h>

//makes color struct
typedef struct {
    int red;
    int green;
    int blue;
} COLOR;

//makes image struct
typedef struct {
    int width;
    int height;
    COLOR *raster;
} IMAGE;


// Creates and returns a pointer to a new blank IMAGE
// with the given dimensions (allocated on the heap)
IMAGE *img_new(int width, int height) {
    IMAGE *img = malloc(sizeof(IMAGE));
    img->width = width;
    img->height = height;
    img->raster = malloc(sizeof(COLOR) * width * height);
    return img;
}

// Frees the memory of the given IMAGE
void img_free(IMAGE *img) {
    free(img->raster);
    free(img);
}

//img ->raster[0].red //if=0, then the red will be removed from that pixel
//this gets the first compoent in raster, gets a color. then pulls red from the first color, raster[0]

IMAGE *img_read(const char *filename) {
//use fopen, fclose, fgets (read one line at a time), sscanf (parse into appropriate integers)
	int width;
	int height;
	FILE *fp = fopen(filename, "r");
	char buffer[80];

	fgets(buffer, 80, fp); //includes new line characters //also this is p3 value so run again
	fgets(buffer, 80, fp);
	sscanf(buffer, "%d %d", &width, &height);
	fgets(buffer, 80, fp); //run again to get the 255 value which is also constant. this means next call will be to color values
	//create blank image
	IMAGE *pic = img_new(width, height);
	//start looping through rest of file which is width*height long and writing to the IMAGE pic.
	for (int i=0; i<width*height; i++) {
		for (int j=0; j<width; j++) {
				
			COLOR c;
			fgets(buffer, 80, fp);
			sscanf(buffer, "%d %d %d", &c.red, &c.green, &c.blue);
		
}}}
	//modify raster
	


//void img_write(IMAGE *img, const char *filename) {
//fopen( , "w")
//fprintf(
int main(int argc, char const *argv[])
{
    if (argc == 3) {
        IMAGE *img = img_read(argv[1]);
        img_gray(img);
        img_write(img, argv[2]);
        img_free(img);
        return 0;
    } else {
        printf("Error! Needs exactly two arguments.\n");
        return 1;
    }
}

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
}