Lesson 9。

09/Exercise01.c

@@ -0,0 +1,40 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int findMaxFirst(int sheep[]) {
+    int max = 0;
+    int i = 0;
+    max = sheep[0];
+    for (i = 1; i < 100; i++) {
+        if (sheep[i] > max) {
+            max = sheep[i];
+        }
+    }
+    return max;
+}
+
+int findMaxRecursive(int sheep[], int start, int prevMax) {
+    if (start == 100) {
+        return prevMax;
+    }
+    else {
+        return findMaxRecursive(sheep, start+1, sheep[start] > prevMax? sheep[start]:prevMax);
+    }
+}
+
+int main() {
+    int sheep[100] = {0};
+    int i = 0;
+    int max1 = 0, max2 = 0;
+    for (i = 0; i < 100; i++) {
+        sheep[i] = rand() % 1000;
+    }
+    // for (i = 0; i < 100; i++) {
+    //     printf("%d\n", sheep[i]);
+    // }
+    max1 = findMaxFirst(sheep);
+    max2 = findMaxRecursive(sheep, 0, 0);
+    printf("By first method, the max is %d\n", max1);
+    printf("By second method, the max is %d", max2);
+    return 0;
+}

09/Exercise02.c

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+#include <stdio.h>
+#include <stdbool.h>
+
+double matA[4][4] = {
+    {1.1161, 0.1254, 0.1397, 0.1490},
+    {0.1582, 1.1675, 0.1768, 0.1871},
+    {0.2368, 0.2471, 0.2568, 1.2671},
+    {0.1968, 0.2071, 1.2168 ,0.2271}
+};
+
+double matB[4] = {
+    1.5471, 1.6471, 1.8471, 1.7571
+};
+
+void rowManipulation(int originRow, double coefficent, int rowBeingAdded) {
+    int col = 0;
+    for (col = 0; col < 4; col++) {
+        matA[rowBeingAdded][col] += matA[originRow][col] * coefficent;
+    }
+    matB[rowBeingAdded] += matB[originRow] * coefficent;
+}
+
+void timesOfRow(int rowCount, double time) {
+    int col = 0;
+    for (col = 0; col < 4; col++) {
+        matA[rowCount][col] *= time;
+    }
+    matB[rowCount] *= time;
+}
+
+int findNoneZeroItem(int startRowIndex, int columnIndex) {
+    bool found = false;
+    int pos = startRowIndex;
+    for (pos = startRowIndex; pos < 4; pos++) {
+        if (matA[pos][columnIndex] != 0) {
+            return pos;
+        }
+    }
+    return -1;
+}
+
+void swapRow(int firstRowIndex, int secondRowIndex) {
+    double temp = 0;
+    int i = 0;
+    for (i = 0; i < 4; i++) {
+        temp = matA[firstRowIndex][i];
+        matA[firstRowIndex][i] = matA[secondRowIndex][i];
+        matA[secondRowIndex][i] = temp;
+    }
+    temp = matB[firstRowIndex];
+    matB[firstRowIndex] = matB[secondRowIndex];
+    matB[secondRowIndex] = temp;
+}
+
+void printOut() {
+    int i = 0, j = 0;
+    for (i = 0; i < 4; i++) {
+        for (j = 0; j < 4; j++) {
+            printf("%lf\t", matA[i][j]);
+        }
+        printf("%lf", matB[i]);
+        printf("\n");
+    }
+}
+
+int main() {
+    int x[4] = {0};
+    int column = 0, row = 0;
+    int tempRow = 0;
+    int noneZeroRow = 0;
+    for (column = 0; column < 4; column++) {
+        noneZeroRow = findNoneZeroItem(row, column);
+        if (noneZeroRow == -1) {
+            continue;
+        }
+        else {
+            swapRow(row, noneZeroRow);
+            timesOfRow(row, 1.0/matA[row][column]);
+            for (tempRow = 0; tempRow < 4; tempRow++) {
+                if (tempRow != row)
+                rowManipulation(row, -matA[tempRow][column], tempRow);
+            }
+            row++;
+        }
+        
+    }
+    for (row = 0; row < 4; row++) {
+        printf("x(%d) = %lf\n", row+1, matB[row]);
+    }
+    return 0;
+}

09/Optional01.c

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+#include <stdio.h>
+#include <stdbool.h>
+
+int history[1000] = {0};
+int nextIndex = 0;
+
+int inHistory(int num) {
+    int i = 0;
+    for (i = 0; i < nextIndex; i++) {
+        if (history[i] == num) {
+            return true;
+        }
+    }
+    return false;
+}
+
+int main() {
+    int input = 0;
+    int sum = 0;
+    int singleDigit = 0;
+    scanf("%d", &input);
+    do {
+        sum = 0;
+        while (input > 0) {
+            singleDigit = input % 10;
+            sum += singleDigit * singleDigit;
+            input /= 10;
+        }
+        input = sum;
+        if (inHistory(sum)) {
+            history[nextIndex] = 0;
+        }
+        else {
+            history[nextIndex] = sum;
+        }
+        nextIndex++;
+    }
+    while (history[nextIndex-1] > 1);
+    printf("%d\n", history[nextIndex-1]);
+    return 0;
+}

09/Optional02.c

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+#include <stdio.h>
+
+void fun(int a[], int n, int flag) {
+    int t, i, j, k;
+    for (i = 0; i < n - 1; i++) {
+        k = i;
+        for (j = i + 1; j < n; j++) {
+            if (flag ? a[k] > a[j]: a[k] < a[j]) {
+                k = j;
+            }
+            if (k != i) {
+                t = a[k];
+                a[k] = a[i];
+                a[i] = t;
+                // Swap a[k] and a[i]
+            }
+        }
+    }
+}
+
+int main() {
+    int c[10] = {8, 6, 7, 10, 9, 3, 5, 2, 4, 1}, i;
+    fun(c, 5, 0);
+    //fun(c + 5, 5, 1);
+    for (i = 0; i < 10; i++) {
+        printf("%d, ", c[i]);
+    }
+
+    //9, 10, 8, 7, 6, 1, 2, 3, 4, 5,
+    //一个莫名其妙的排序，它不一定能给出正确的顺序。
+    //老师出这个题的意义可能只是想强调c是一个指针，加5就代表着c[5]的地址？
+    return 0;
+}

09/Optional03.c

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+#include <stdio.h>
+
+int main() {
+    char idCardNo[18] = {0};
+    int i = 0, sum = 0;
+    int temp = 0;
+    char checkSum = 0;
+    int weigh[17] = {7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2};
+    for (i = 0; i < 18; i++) {
+        idCardNo[i] = getchar();
+    }
+    for (i = 0; i < 17; i++) {
+        temp = ((idCardNo[i] - '0')*weigh[i]) % 11;
+        sum += ((idCardNo[i] - '0')*weigh[i]) % 11;
+    }
+    checkSum = (12 - (sum % 11)) % 11;
+    if (checkSum == 10) {
+        checkSum = 'X';
+    }
+    else {
+        checkSum += '0';
+    }
+    if (checkSum == idCardNo[17]) {
+        printf("合法\n");
+    }
+    else {
+        printf("非法，正确校验位是%c", checkSum);
+    }
+    return 0;
+}