new file: 19_PRACTICESET2.c

	new file:   20_arrays.c
	new file:   21_PRACTICESET3.c
	new file:   22_pointers.c
	new file:   23_pointers.c
	new file:   24_null_pointer.c
	new file:   25_pointer_arithematic.c
	new file:   26_strings.c
	renamed:    8_P1_multiplication_table.c -> 8_PRACTICESET1.c

Author: DeveloperAmrit

Diff for: 19_PRACTICESET2.c

@@ -0,0 +1,99 @@
+#include <stdio.h>
+#include <string.h>
+#include <math.h>
+#include <stdlib.h>
+
+int main()
+{
+    // taking input string
+    char input[1000];
+    printf("Input format <number>$<unit in lowercase>\n");
+    scanf("%s", input);
+
+    // taking to which input string
+    char toUnit[100];
+    printf("To which unit\n");
+    scanf("%s", toUnit);
+
+    // in = input number (float) , unit is unit of input number
+    float in = 0;
+    char unit[100] = {0};
+
+    // a for detecting $ sign
+    int a = 1;
+
+    // just for iteration
+    int j = 0;
+    int k = 0;
+
+    // string storing the number
+    char forn[100];
+
+    for (int i = 0; i < strlen(input); i++)
+    {
+        if (a)
+        {
+            if (input[i] == '$')
+            {
+                a = 0;
+                continue;
+            }
+            forn[k++] = input[i];
+        }
+        else
+        {
+            unit[j++] = input[i];
+        }
+    }
+
+    // convertign string to float
+    char *endPtr;
+    in = strtof(forn, &endPtr);
+
+    // terminating unit as its length was 100
+    unit[j] = '\0';
+
+    // iur = input unit row
+    int iur = -1;
+    int iuc = -1;
+
+    int numOfCols = 16; 
+    char *DISTANCE_UNITS[][16] = {{"pm","/","/","nm","/","/","um","/","/","mm", "cm", "dm", "m", "dam", "hm", "km"},
+                                 {"pg","/","/","ng","/","/","ug","/","/","mg", "cg", "dg", "g", "dag", "hg", "kg"},
+                                 {"pl","/","","nl","/","/","ul","/","/","ml", "cl", "dl", "l", "dal", "hl", "kl"}};
+
+    for (int i = 0; i < 3; i++)
+    {
+        for (int j = 0; j < numOfCols; j++)
+        {
+            if (!strcmp(unit, DISTANCE_UNITS[i][j]))       // strcmp return 0 for same strings
+            {
+                iur = i;
+                iuc = j;
+            }
+        }
+    }
+    // the ouput float out;
+    float out = in * 1.0;
+
+    // our = output unit row
+    int our = -1;
+    int ouc = -1;
+
+    for (int i = 0; i < 3; i++)
+    {
+        for (int j = 0; j < numOfCols; j++)
+        {
+            if (!strcmp(toUnit, DISTANCE_UNITS[i][j]))       
+            {
+                our = i;
+                ouc = j;
+                if (iuc != -1)
+                {
+                    out = in * pow(10, (iuc - ouc));
+                }
+            }
+        }
+    }
+    printf("%f %s",out,toUnit);
+}

Diff for: 20_arrays.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+
+void printMatrix(int rows,int columns,int matrix[rows][columns]);
+
+int main(){
+    int n;
+    scanf("%d",&n);
+
+    int arr1[n][n];
+    for(int i=0;i<n;i++){
+        for(int j=0;j<n;j++){
+            scanf("%d",&arr1[i][j]);
+        }
+    }
+
+    printMatrix(n,n,arr1);
+    
+}
+
+
+
+void printMatrix(int rows,int columns, int matrix[rows][columns]){
+    for(int i=0;i<rows;i++){
+        printf("|");
+        for(int j=0;j<columns;j++){
+            printf(" %d",matrix[i][j]);
+        }
+        printf(" |\n");
+    }
+}

Diff for: 21_PRACTICESET3.c

@@ -0,0 +1,18 @@
+#include <stdio.h>
+
+int fabbonachi(int);
+
+int main(){
+    int n;
+    scanf("%d",&n);
+    printf("%dth fabbonachi is %d",n,fabbonachi(n));
+}
+
+int fabbonachi(int n){
+    if(n==1 || n==0){
+        return n;
+    }
+    else{
+        return fabbonachi(n-1)+fabbonachi(n-2);
+    }
+}

Diff for: 22_pointers.c

@@ -0,0 +1,19 @@
+#include <stdio.h>
+
+int main(){
+    int n=10;
+    int *pn = &n;
+
+    printf("The value of n is %d",n);
+    printf("\nThe address of n is %x",pn);                           // %x for hexdecimal
+    printf("\nThe value at address %x is %d",pn,*pn);
+}
+
+
+/**
+Use of pointers :
+> Dynamic memory allocation
+> Arrays, functions and structures
+> Return multiple values from a function
+> pointer reduces the code and improves the perfomance
+ */

Diff for: 23_pointers.c

@@ -0,0 +1,42 @@
+
+// pointer is a varible which store address of another variable
+// types of pointer = type of varibale whose address it is storing
+// types of pointer = int, float, char, array, string, function
+// decleared with * sign
+
+// a pointer can also store address of other pointer
+
+#include <stdio.h>
+
+int main(){
+    int n = 6;
+    int *ptr;               // * is just syntax for pointer, * donot have any role like indirection operator
+    ptr = &n;
+
+    scanf("%d",ptr);       // no & required, add we are giving the adress of n
+
+    printf("%d",n);        // prints value of n
+
+    printf("\n%d",ptr);    // prints adress of n which is the value of ptr
+
+    printf("\n%d",*ptr);     // prints value of n, * working as its role of indirection operator
+
+    int a = 3;
+    int b = *&a;
+    printf("\n%d == %d",a,b);     // b==a
+
+}
+
+// &amrit = address of amrit 
+// *a = program treats value of a as an adress of some other variable and search for this address and goes for that varible's value
+// * is called indirection operator
+
+// int *p = &a : decleration and assignment of pointer
+// p : address of a
+// *p : follow address
+
+// * and & are just opposite of each other
+// int *i = &a;
+// int j = *i      // j==a
+
+// int* a is same as int *a

Diff for: 24_null_pointer.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+
+int main(){
+    // int n = NULL; cannot do this
+
+    int *ptr = NULL;
+    printf("%d %d",ptr);
+}
+
+// Null pointer : pointer not assigned any value (NULL)
+// Used to prevent garbage values

Diff for: 25_pointer_arithematic.c

@@ -0,0 +1,10 @@
+#include <stdio.h>
+
+int main(){
+    int a = 34;
+    int *pa = &a;
+
+    printf("%d\n",pa);
+    printf("%d",pa+1);
+    return 0;
+}

Diff for: 26_strings.c

@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <string.h>       // for strlen and strcpy
+#include <stdlib.h>       // for malloc
+
+int main(){
+
+    // 1 Array type string decleration
+
+    char str1[20] = "Hello";                // 'Hello' + '\0'  
+    printf("%s",str1);
+    printf("\n%d",strlen(str1));           // strlen doesnot count the null terminator in length of string
+    /*
+    Here, "Hello" takes 6 spaces (5 characters + 1 null terminator), and the remaining 14 elements of the array are uninitialized.
+    strlen will return 5, it doesnot count null terminator
+    */
+
+    // 2 Array type string decleration without array length
+
+    char str2[] = "Hwllo";         // Equivalent to str[6] = "Hwllo"  
+    printf("\n%s",str2);
+    printf("\n%d",strlen(str2));
+
+    // yes the declration length counts the null character  but strlen donot
+
+    // 3 Pointer to a string 
+
+    char *str3 = "Helloworld";       // points to a string located in read-only memory
+    printf("\n%s",str3);
+    printf("\n%d",strlen(str3));
+
+    // cannot modify str3 later as readonly memory
+
+    // 4 Array of individual characters
+
+    char str4[6] = {'A', 'm', 'r', 'i', 't', '\0'};
+    printf("\n%s",str4);
+    printf("\n%d",strlen(str4));
+
+    // 5 strcpy method
+
+    char str5[6];
+    strcpy(str5,"Aloka");
+
+    printf("\n%s",str5);
+    printf("\n%d",strlen(str5));
+
+    // 6 Dynmaic allocation of strings
+
+    char *str6 = (char *)malloc(6*sizeof(char));
+    strcpy(str6,"Hallo");
+    printf("\n%s",str6);
+    printf("\n%d",strlen(str6));
+
+    // donot forget to free the memeory
+    free(str6);
+
+
+    return 0;
+
+
+}
+
+/**
+ * String is not a datatype in c.
+ * We represent string as an array of characters ending with Null terminator \0
+ */