finished solutions to Chapter 2

Author: satyajitghana

Diff for: Chapter-2/Exercise 2-10/lower.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <ctype.h>
+#define MAXLINE 1000
+
+int _getline(char line[], int maxline);
+void lower(char line[]);
+
+int main() {
+    int len;
+    char line[MAXLINE];
+    while ((len = _getline(line, MAXLINE)) > 0) {
+        lower(line);
+        printf("%s", line);
+    }
+    return 0;
+}
+
+void lower(char line[]) {
+    int i = 0;
+    while (line[i] != '\0') {
+        line[i] = (isalpha(line[i])) ? ((isupper(line[i])) ? (line[i]+32) : (line[i])) : (line[i]);
+        i++;
+    }
+}
+
+int _getline(char s[], int lim) {
+    int c, i;
+    for (i = 0 ; i < lim-1 && (c = getchar()) != EOF && c != '\n'; i++)
+        s[i] = c;
+    if (c == '\n') {
+        s[i++] = c;
+    }
+    s[i] = '\0';
+    return i;
+}

Diff for: Chapter-2/Exercise 2-4/squeeze.c

@@ -0,0 +1,41 @@
+#include <stdio.h>
+#define MAXLINE 1000
+
+int _getline(char line[], int maxline);
+void squeeze(char string1[], char string2[]);
+
+int main() {
+    // take two lines as input
+    int len1, len2;
+    char line1[MAXLINE], line2[MAXLINE];
+    while ((len1 = _getline(line1, MAXLINE)) > 0 && (len2 = _getline(line2, MAXLINE)) > 0) {
+        squeeze(line1, line2);
+        printf("%s", line1);
+    }
+    return 0;
+}
+
+// deletes every character in s1 that matches any of the character in s2
+void squeeze(char s1[], char s2[]) {
+    int i, j;
+    for (i = j = 0 ; s1[i] != '\n' && s1[i] != '\0' ; i++) {
+        int FOUND = 0;
+        for (int k = 0 ; s2[k] != '\n' && s2[k] != '\0' ; k++) {
+            if (s1[i] == s2[k]) {FOUND = 1; break;}
+        }
+        if (!FOUND) s1[j++] = s1[i];
+    }
+    s1[j++] = '\n';
+    s1[j] = '\0';
+}
+
+int _getline(char s[], int lim) {
+    int c, i;
+    for (i = 0 ; i < lim-1 && (c = getchar()) != EOF && c != '\n'; i++)
+        s[i] = c;
+    if (c == '\n') {
+        s[i++] = c;
+    }
+    s[i] = '\0';
+    return i;
+}

Diff for: Chapter-2/Exercise 2-5/any.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#define MAXLINE 1000
+
+int _getline(char line[], int maxline);
+int any(char string1[], char string2[]);
+
+int main() {
+    // take two lines as input
+    int len1, len2;
+    char line1[MAXLINE], line2[MAXLINE];
+    while ((len1 = _getline(line1, MAXLINE)) > 0 && (len2 = _getline(line2, MAXLINE)) > 0) {
+        // we get the location of the first character in line1 that matches any of the character in line2
+        int loc = any(line1, line2);
+        if (loc != -1) printf("Location : %d\n", loc);
+        else printf("character not found\n");
+    }
+    return 0;
+}
+
+int any(char s1[], char s2[]) {
+    for (int i = 0 ; s1[i] != '\n' && s1[i] != '\0'; i++) {
+        for (int j = 0 ; s2[j] != '\n' && s2[j] != '\0'; j++) {
+            if (s1[i] == s2[j]) return i;
+        }
+    }
+    return -1;
+}
+
+int _getline(char s[], int lim) {
+    int c, i;
+    for (i = 0 ; i < lim-1 && (c = getchar()) != EOF && c != '\n'; i++)
+        s[i] = c;
+    if (c == '\n') {
+        s[i++] = c;
+    }
+    s[i] = '\0';
+    return i;
+}

Diff for: Chapter-2/Exercise 2-6/setbits.c

@@ -0,0 +1,30 @@
+#include <stdio.h>
+
+int setbits(int x, int pos, int n, int y);
+
+int main() {
+     // let x be 10101011
+    int x = 171;
+    // let y be 11111111
+    int y = 255;
+
+    //let position be 3, and 3 bits to be copied
+    int p = 3;
+    int n = 3;
+
+    // result must be 11111101
+    printf("%d\n", setbits(x, p, n, y));
+
+    return 0;
+}
+
+setbits(x, p, n, y) {
+    // push n bits from pth position of x to the right and clear other bits
+    int tmp1 = (x >> (p-n+1)) & ~(~0<<n);
+    // erase the last n bits in y
+    int tmp2 = y & (~0 << n);
+    // now just OR the two together
+    int res = tmp1 | tmp2;
+
+    return res;
+}

Diff for: Chapter-2/Exercise 2-7/invert.c

@@ -0,0 +1,26 @@
+#include <stdio.h>
+
+int invert(int x, int pos, int n);
+
+int main() {
+     // let x be 10101011
+    int x = 171;
+
+    //let position be 3, and 3 bits to be inverted
+    int p = 3;
+    int n = 3;
+
+    // result must be 10100101
+    printf("%d\n", invert(x, p, n));
+
+    return 0;
+}
+
+int invert(int x, int p, int n) {
+    int MASK = (~0<<(p+1)) | ~(~0<<(p-n+1));
+    int tmp1 = ~(x & ~(MASK));
+    int tmp2 = (x & (MASK)) | ~MASK ;
+    printf("%d %d %d\n", MASK, tmp1, tmp2);
+    int res = tmp1 & tmp2;
+    return res;
+}

Diff for: Chapter-2/Exercise 2-8/rightrot.c

@@ -0,0 +1,28 @@
+#include <stdio.h>
+
+unsigned int rightrot(unsigned int x, int n);
+
+int main() {
+     // let x be 00000000000000000000000010101011
+    unsigned int x = 171;
+    int n = 4;
+
+    // result must be 10110000000000000000000000001010
+    printf("%u\n", rightrot(x, n));
+
+    return 0;
+}
+
+unsigned int rightrot(unsigned int x, int n) {
+    for (int i = 0 ; i < n ; i++) {
+        if (x & 1 == 1) {
+            //putchar('*');
+            x = x >> 1;
+            x = x | ~(~0U >> 1);
+        } else {
+            //putchar('_');
+            x = x >> 1;
+        }
+    }
+    return x;
+}

Diff for: Chapter-2/Exercise 2-9/bitcount.c

@@ -0,0 +1,22 @@
+#include <stdio.h>
+
+int bitcount(unsigned x);
+
+int main() {
+     // let x be 10101011
+    unsigned x = 171;
+
+    // result must be 5
+    printf("%d\n", bitcount(x));
+
+    return 0;
+}
+
+int bitcount(unsigned x) {
+    int b = 0;
+    while (x) {
+        x &= (x-1);
+        b++;
+    }
+    return b;
+}