c study

Author: wenjun1055

.gitignore

@@ -23,3 +23,4 @@ thread4
 thread
 thread1
 thread5
+*.dSYM

6.1.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+#include <assert.h>
+
+char *find_char(char *source, char *chars);
+
+int main()
+{
+    char *source = "ABCDEF";
+    char *chars  = "ESmSG";
+    char *result;
+    result = find_char(source, chars);
+    printf("%c\r\n", *result);
+
+    return 0;
+}
+
+char *find_char(char *source, char *chars)
+{
+    assert(source != NULL);
+    assert(chars != NULL);
+
+    while (*source != '\0') {
+        
+        char *char_tmp = chars;
+
+        while (*char_tmp != '\0') {
+            if (*source == *char_tmp) {
+                return source;
+            }
+
+            char_tmp++;
+        }
+
+        source++;
+    }
+
+    return "\r\0";
+}

6.2

@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+int del_substr(char *str, char *substr);
+int find_str(char *str, char *substr);
+
+int main()
+{
+    char *str = "ABCDEFGHIJK";
+    char *substr = "DBCD";
+
+    printf("%d", find_str(str, substr));
+
+    if (! find_str(str, substr)) {
+        printf("not exists substr in str\r\n");
+        return 0;
+    }
+
+
+}
+
+int find_str(char *str, char *substr)
+{
+    int counter = 0;
+
+    assert(str != NULL);
+    if (substr == NULL) {
+        return 1;
+    }
+
+    while (*str != '\0') {
+        char str_char = *str;
+        char substr_char = *substr;
+
+        if (str_char == substr_char) {
+            while (1) {
+               str_char = *++str;
+               substr_char = *++substr;
+               
+               if (str_char != substr_char && substr_char != '\0') {
+                    break;
+                }
+
+               if ((str_char != substr_char && substr_char == '\0') || (str_char == substr_char && substr_char == '\0')) {
+                    return 1;
+                }
+            }
+        }
+
+        str++;
+    }
+
+    return 0;
+}
+

6.2.c

@@ -0,0 +1,35 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+void reverse_string(char *string);
+
+int main()
+{
+    char *string = "ABCDEFG";
+    printf("Origion:%s", string);
+    reverse_string(string);
+    string = strrev(*string);
+    printf("Change:%s", string);
+
+    return 0;
+}
+
+void reverse_string(char *string)
+{
+    char *h = string;
+    char *t = string;
+    char ch;
+
+    while(*t++){};
+    t--;
+    t--;
+
+    while(h < t) {
+        ch = *h;
+        *h++ = *t;
+        *t-- = ch;
+    }
+
+    //return string;
+}

6.3.c

@@ -0,0 +1,31 @@
+#include <stdio.h>
+
+int gcd(int m, int n);
+
+int main()
+{
+    int m,n,max;
+    printf("Please input m and n:");
+    scanf("%d,%d", &m, &n);
+    max = gcd(m, n);
+    printf("max = %d\r\n", max);
+
+    return 0;
+}
+
+int gcd(int m, int n)
+{
+    if (0 >= m || 0 >= n) {
+        return 0;
+    }
+
+    int r = m % n;
+
+    if (r == 0) {
+        return n;
+    }
+
+    if (r > 0) {
+        return gcd(n, r);
+    }
+}

7.1.2

@@ -0,0 +1,22 @@
+#include <stdio.h>
+
+int main()
+{
+    int max,m,n;
+    printf("Please input m and n:");
+    scanf("%d,%d",&m, &n);
+
+    if (0 >= m || 0 >= n) {
+        max = 0;
+    }
+
+    max = m % n;
+    while (max > 0) {
+        m = n;
+        n = max;
+
+        max = m % n;
+    }
+
+    printf("%d\r\n", n);
+}

7.2.1.c

@@ -0,0 +1,29 @@
+#include <stdio.h>
+#include <stdarg.h>
+
+int max_list(int start, ...);
+
+int main()
+{
+    printf("max is %d\r\n", max_list(5,11,2,56,34,999,32,-1));
+
+    return 0;
+}
+
+int max_list(int start, ...)
+{
+    va_list var_arg;
+    int count;
+    int i = 0, max, current;
+
+    va_start(var_arg, start);
+    max = start;
+
+    do {
+        current = va_arg(var_arg, int);
+        if (current > max)
+            max = current;
+    } while(current > 0);
+    
+    return max;
+}

7.2.2

@@ -0,0 +1,22 @@
+#include <stdio.h>
+#include <string.h>
+
+int main()
+{
+    char *a = "abcd";
+    char *b = "abcde";
+    
+    if (strlen(a) > strlen(b)) {
+        printf("1\r\n");
+    } else {
+        printf("2\r\n");
+    }
+
+    //stlen的结果是个无符号数，所以操作符>=左边的表达式也将是无符号数
+    //而无符号数绝不可能是负的
+    if (strlen(a) - strlen(b) >= 0) {
+        printf("3\r\n");
+    } else {
+        printf("4\r\n");
+    }
+}