diff --git a/4.c b/4.c
new file mode 100644
index 0000000..b6202a7
--- /dev/null
+++ b/4.c
@@ -0,0 +1,31 @@
+
+
+#include<stdio.h>
+#include<string.h>
+int main()
+{
+char str[100];
+int table[4][2]={{1,0},{2,0},{3,0},{3,3}};
+int s=0,i,l;
+printf("\nenter the string\n");
+scanf("%s",str);
+l= strlen(str);
+for(i=0;i<l;i++)
+{
+s=table[s][str[i] -'0'];
+}
+if(s==0 || s==1 || s==2)
+printf("string is valid\n");
+else 
+printf("string is invalid\n");
+}
+
+/*Output:
+enter the string
+1001000010
+string is invalid
+
+enter the string
+001001001
+string is valid
+*/