Lesson 2.

02/Exercise01.c

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+#include <stdio.h>
+int main() {
+    short a = 10;
+    int b = 100;
+    int short_length = sizeof a;
+    int int_length = sizeof(b);
+    int long_length = sizeof(long);
+    int char_length = sizeof (char) ;
+    printf("short=%d, int=%d, long=%d, char=%d\n", short_length,
+    int_length, long_length, char_length);
+    return 0;
+}

02/Exercise02.c

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+#include <stdio.h>
+int main() {
+    int m = 306587;
+    long n = 28166459852;
+    printf("m=%hd, n=%hd\n", m, n);
+    printf("n=%d\n", n);
+    return 0;
+}

02/Exercise03.c

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+#include <stdio.h>
+int main() {
+    char input, prev, next;
+    input = getchar();
+    prev = input - 1;
+    next = input + 1;
+    printf("ASCII number: %d, Previous char: %c, Next char: %c", input, prev, next);
+    return 0;
+}

02/Experiment1-2.c

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+#include <stdio.h>
+int main() {
+    int x1, x2; // Define two integers; uses 4 bytes each.
+    unsigned y; // Define an unsigned integer; uses 4 bytes.
+    char c1, c2; // Define two charater; uses 1 bytes each.
+    x1 = 65535;
+    x2 = x1 + 5;
+    printf("Enter y: ");
+    scanf("%u", &y); // Read y from user input
+    c1 = 97;
+    c2 = 'A';
+    c2 = c2 + 32; //Change the value of c2, using c2 itself.
+    printf("x1=%d\n", x1);
+    printf("x2=%d\n",x2);
+    printf("y=%u\n",(y+15)); // Calculate y + 15, and then output it
+    printf("c1=%c\n",c1);
+    printf("c2=%c\n",c2);
+    return 0;
+}

02/Optional-2.c

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+#include <stdio.h>
+
+// Code for encrypting
+void encryptDecrypt(int mode) {
+    char input[100] = {0}; //Maximum length of the string is 100 characters
+    short pass; //Password should be within range 0~25
+    if (mode == 0) {
+        printf("Enter the string to be encrypted (no longer than 100 characters):\n");
+    }
+    else {
+        printf("Enter the string to be decrypted (no longer than 100 characters):\n");
+    }
+    scanf("%s",input);
+    printf("Enter your password (0-25): ");
+    scanf("%hd", &pass);
+    // Go through every character in input
+    for (int i = 0; i < 100; i++){
+        if (input[i] == '\0') {
+            // '\0' means we have reached the string's end.
+            break;
+        }
+        else {
+            input[i] -= 'A'; //Calculate the chacter's place in the alphabet, from 0~25
+            if (mode == 0) {
+                input[i] += pass; //Add the offset of pass
+            }
+            else {
+                input[i] -= pass; //Subtract the offset of pass
+                input[i] += 26; //Avoid negative number
+            }
+            input[i] %= 26; //Prevent the number from overflow
+            input[i] += 'A'; //Turn the number into ASCII again.
+            printf("%c", input[i]);
+        }
+    }
+}
+
+int main() {
+    char mode;
+    printf("Slect Mode: (1) Encypt (2) Decrypt: ");
+    mode = getchar();
+    if (mode == '1') {
+        encryptDecrypt(0);
+    }
+    else if (mode == '2') {
+        encryptDecrypt(1);
+    }
+    else {
+        printf("Unrecognized command.");
+    }
+    return 0;
+}