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Lab9/task3.c

+#include <stdio.h>
+#include <ctype.h>
+#include <string.h>
+int isint(char a);
+
+int main(){
+	char string[100];
+	int len,
+		i;
+	do{
+		puts("please input an integer.");
+		scanf("%s", string);
+		len = strlen(string);
+		for(i = 0; i < len; i++){
+			if(isint(string[i]) == 0){
+				puts("input is not an integer");
+				break;
+			}
+		}
+	}while(i < len);
+	
+	puts("the input is an integer");
+	
+	return 0;
+}
+
+int isint(char a){
+	int result = isdigit(a);
+	return result;
+}