add xunhuan3-4

Code/test.c

@@ -0,0 +1,10 @@
+#include<stdio.h>
+
+int main()
+{
+    
+
+
+    
+    return 0;
+}

Code/xunhuan1.c

@@ -2,11 +2,12 @@
 
 int main()
 {
-    int x = 0,i = 0;
+    int sum = 0,i = 1;
-    for(i = 1; i <= 100; i++)
+    while(i <= 100)
     {
-        x += i;
+        sum += i;
+        i++;
     }
-    printf("%d\n", x);
+    printf("%d\n", sum);
     return 0;
 }

Code/xunhuan2.c

@@ -19,5 +19,19 @@ int main()
         }
     }
 
+    /*
+    while(1)
+    {
+        printf("请输入两个整数:\n");
+        scanf("%d %d", &x , &y);
+        if(x == y)
+        {
+            printf("%d = %d\nexit\n",x,y);
+            break;
+        }
+        x > y ? printf("%d更大\n", x) : printf("%d更大\n", y);
+        
+    }*/
+
     return 0;
 }

Code/xunhuan3.c

@@ -0,0 +1,27 @@
+#include <stdio.h>
+
+int main()
+{
+	int n,i,j;
+
+    for(j=0;j<5;j++)
+    {
+        printf("请输入第%d个数：\n",j+1);
+
+        scanf("%d",&n);
+        
+        if(n<2)
+        {
+            printf("%d不是素数\n",n);
+            continue;
+        }
+        for(i=2;i<n;i++)
+            if(n%i==0)
+                break;
+        if(i<n)
+            printf("%d不是素数\n",n);
+        else
+            printf("%d是素数\n",n); 
+    }
+	return 0;
+} 

Code/xunhuan4.c

@@ -0,0 +1,38 @@
+#include <stdio.h>
+
+int main() 
+{
+    int n; //菱形的一半高度
+    int i, j;
+    printf("请输入菱形的高度：");
+    scanf("%d", &n);
+    //上半
+    for (i = 1; i <= n; i++)
+    {
+        for (j = i; j < n; j++) 
+        {
+            printf(" ");
+        }
+        for (j = 1; j <= (2 * i - 1); j++)
+        {
+            printf("*");
+        }
+        printf("\n");
+    }
+
+    //下半
+    for (i = n - 1; i >= 1; i--)
+    {
+        for (j = n; j > i; j--)
+            {
+                printf(" ");
+            }
+        for (j = 1; j <= (2 * i - 1); j++)
+            {
+                printf("*");
+            }
+        printf("\n");
+    }
+
+    return 0;
+}