/* Write and read a binary file (fwrite and fread) */
 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
#define LEN 50
#define N_STUD 2
 
typedef struct stud{
  char name[LEN+1];
  unsigned int id;
  float average;
}stud_t;
 
 
int main() {
  FILE *fp;
  stud_t student[N_STUD];
  int i;
  char row[LEN+1];
  unsigned int n_stud;
 
  strcpy(student[0].name, "Steven");
  student[0].id = 120000;
  student[0].average = 25.5;
 
  strcpy(student[1].name, "Julia");
  student[1].id = 120001;
  student[1].average = 28.5;
 
  fp = fopen("out.bin", "w"); /* Open the file for writing */
  if (fp == NULL){
    printf("Error: file out.bin cannot be opened\n");
    exit(1);
  }
 
 
  /* Write the file */
  /* NOTE 2: a binary file sometimes cannot be readable 
     correctly in a PC that it is not the one which generates it, 
     because, for instance, integer numbers can be coded with a
     different number of bytes.
  */
 
  /* Write in binary all the data contained in the structure */
  fwrite(student, sizeof(stud_t), N_STUD, fp); 
 
  /* DIMENSION OF THE GENERATED FILE
     The dimension of the generated file will be:
     n_stud*sizeof(stud_t)
     in the case of the computer used to test the program:
     2*60 = 120 byte
   */
 
  fclose(fp); /* Close the file */
 
 
 
  fp = fopen("out.bin", "r"); /* Open the file for reading */
  if (fp == NULL){
    printf("Error: file out.bin cannot be opened\n");
    exit(1);
  }
 
  /* Read the file */
  n_stud = 0;
  while( fread(&student[n_stud], sizeof(stud_t), 1, fp) == 1 ) {
    n_stud++;
  }
 
  fclose(fp); /* Close the file */
 
 
  /* Print the read records */
  for (i=0; i<n_stud; i++) {
    printf("%s %d %f\n", student[i].name, student[i].id, student[i].average);
  }
 
 
  return 0;
}

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
}