c basics and other

Author: randios

c/basics/arithmetics.c

@@ -0,0 +1,52 @@
+#include <stdlib.h>
+#include <math.h>
+
+10 + 20                         // 30
+20 - 10                         // 10
+10 * 20                         // 200
+20 / 10                         // 2
+
+// power require math.h
+pow(10, 2)                      // 100.00000
+
+// floating point conversion
+10.0 + (10 + 20)                // 40.000000
+
+// NOTE: char is promoted to int value
+'c' + 10
+// 109 (ascii value of c is 99)
+
+// floating point conversion using type casting
+(double) 10.0 + (10 + 20)       // 40.000000
+(double) 20.0 - (10 + 10)       // 0.000000
+(double) 10.0 * (10 * 2)        // 200.000000
+
+// common division error
+30 / 20                         // 1
+(double) 30 / 20                // 1.500000
+
+// integer divison, quotient
+20 / 20                         // 1
+30 / 20                         // 1
+40 / 20                         // 2
+
+// modulo, remainder
+10 % 20                         // 10
+
+// module, remainder on floating point
+fmod(12.5, 10.0)                // 2.500000
+
+// built-ins
+abs(-20)                        // 20
+
+// rounding value
+round(2.945)                    // 3.000000
+round(2.495)                    // 2.000000
+
+// NOTE: no built-ins for round to decimal places
+
+// increment and decrement
+int a = 10;
+
+a++                             // 11
+a--                             // 9

c/basics/arrays.c

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+#define MAX_STRING_SIZE 40
+
+// arrays are mutable
+double array_one[] = { 200.0, -2.2, 1.0, 0.0 };
+char array_two[][MAX_STRING_SIZE] = { "REMOVE", "RANDOM" };
+
+array_one[0]                    // 200.000000
+array_two[1]                    // RANDOM
+
+array_one[0] = 50.0;
+array_one[0]                    // 50.000000
+
+// multi-dimensional array
+int array_multi[2][10] = {
+    { 0, 1, 2, 3, 4 },
+    { 5, 6, 7, 8, 9 }
+};
+
+array_multi[1][2]
+// 7
+
+// NOTE: no built-ins for length
+
+// calculate length based on type
+int length = sizeof(array_one) / sizeof(double);
+length
+// 4

c/basics/constants.c

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+// OUTSIDE SCOPE: define constants
+#define LENGTH 10
+#define WIDTH 5
+
+// INSIDE SCOPE: define constants
+const int LENGTH = 10;
+const int WIDTH = 5;

c/basics/error-handling.c

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+#include <errno.h>
+
+// OUTSIDE SCOPE: define error variable
+extern int errno;
+
+// INSIDE SCOPE: handle error
+FILE *file;
+
+int errnum;
+file = fopen("file.txt", "rb");
+
+// error returns -1 or NULL
+if (file == NULL) {
+    // error code is stored in errno
+    errnum = errno;
+
+    // print error code
+    fprintf(stderr, "Error code: %d\n", errno);
+
+    // perror: print string representation of error code
+    perror("Error as printed by perror");
+
+    // strerror: print pointer to string representation of error code
+    fprintf(stderr, "Error opening file: %s\n", strerror(errnum));
+} else {
+    fclose(file);
+}
+
+// EXAMPLE: divide by zero
+int dividend = 10;
+int divisor = 2;
+int quotient;
+
+// check if divisor is zero
+if (divisor == 0) {
+    fprintf(stderr, "%s\n", "Division by zero, exiting...");
+    
+    // exit as failure
+    exit(EXIT_FAILURE);
+}
+
+quotient = dividend / divisor;
+fprintf(stderr, "Quotient: %d\n", quotient);
+// 5
+
+// exit as success
+exit(EXIT_SUCCESS);

c/basics/files.c

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+FILE *file;
+
+// write to file
+file = fopen("test.txt", "w+");
+fprintf(file, "%s\n", "This is a string.");
+
+// close file
+fclose(file);
+
+// read a file
+char buffer[255];
+
+file = fopen("test.txt", "r");
+
+// stops at first space
+fscanf(file, "%s\n", buffer);
+printf("%s\n", buffer);
+// This
+
+// stops at newline
+fgets(buffer, 255, (FILE*)file);
+printf("%s\n", buffer);
+// is a string.

c/basics/for-loop.c

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+int a;
+for (a = 1; a < 5; a++) {
+    // do something
+}
+
+// iterate array
+#define ARRAY_SIZE 5
+
+int array[ARRAY_SIZE] = { 1, 2, 3, 4, 5 };
+
+int n;
+for (n = 0; n < ARRAY_SIZE; n++) {
+    // do something
+}
+
+// nested
+int i;
+int j;
+
+for (i = 0; i < 2; i++) {
+    for (j = 0; j < 2; j++) {
+        // do something
+    }
+}

c/basics/functions.c

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+// declare function
+// NOTE: needs to be BEFORE main() when functions are DEFINED AFTER main()
+int function(int arg);
+
+// define function
+int function(int arg) {
+    // do something
+    return 0;
+}
+
+// EXAMPLE: power function
+
+// declare function
+int power(int base, int x);
+
+// main() function
+int main(void) {
+    // call function
+    power(2, 3)                 // 8
+
+    return 0;
+}
+
+// define function
+int power(int base, int x) {
+    /* multiply base with itself x times */
+
+    int result = 1;
+
+    int i;
+    for (i = 0; i < x; i++) {
+        result = result * base;
+    }
+
+    return result;
+}
+
+// END EXAMPLE
+
+// variable arguments
+#include <stdarg.h>
+
+// OUTSIDE SCOPE: define function with variable arguments
+double average(int n, ...) {
+    // require stdarg.h
+    va_list valist;
+
+    double sum = 0.0;
+    int i;
+
+    // initialise valist for n arguments
+    va_start(valist, n);
+
+    // access arguments assigned to valist
+    for (i = 0; i < n; i++) {
+        sum += va_arg(valist, int);
+    }
+
+    // clean memory reserved for valist
+    va_end(valist);
+
+    return sum / n;
+}
+
+// INSIDE SCOPE: use function
+printf("Average of 2, 3, 4, 5: %f\n", average(2, 3, 4, 5));
+// Average of 2, 3, 4, 5: 3.500000

c/basics/header.c

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+// FILE: header.h
+const int number = 10;
+
+// FILE: header.c
+
+// include header
+#include "header.h"
+
+printf("%d\n", number);
+// 10

c/basics/header.h

@@ -0,0 +1,2 @@
+// FILE: header.h
+const int number = 10;

c/basics/if-else.c

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+int a = 1;
+
+if (a < 1) {
+    // do something
+} else if (a == 1) {
+    // do something
+} else {
+    // do something
+}
+
+// single line expression
+(a < 1) ? "a is smaller" : "a is not smaller";
+// a is not smaller