当输入无效值时，用户必须重试C中的新值

对于我的硬件分配，我必须创建一个程序，根据用户输入输出一个基于星号的三角形。我已经让我的程序在用户输入一个整数时工作，输出正确的三角形，但我的问题是当输入一个无效值时，我如何使它工作，以便用户必须重新尝试提交一个值？我查看了论坛，没有找到类似的问题

#include <stdio.h>

int main() {
int lines, a, b;

//prompt user to input integer
printf("Input a value from 1 to 15: ");
scanf("%d", &lines);

//Check if inputed value is valid
if(lines >= 1 && lines <= 15) {
    /*create triangle based on inputed value */
    for(a = 1; a <= lines; a++) {
        for(b=1; b<= a; b++) {
            printf("*");
        }
        printf("\n");
    }
}
else {
    printf("not valid");/* repeat code in this else statement, maybe */
}
system("pause");
}

你可以用doo。。while循环向用户请求有效输入。代码

int main() { 
   int lines, a, b;

    do {

        //prompt user to input integer
        printf("Input a value from 1 to 15: ");
        scanf("%d", &lines);

        //Check if inputed value is valid
        if(lines >= 1 && lines <= 15) {
            /*create triangle based on inputed value */
           for(a = 1; a <= lines; a++) {
                for(b=1; b<= a; b++) {
                   printf("*");
               }
               printf("\n");
           }

           break; //break while loop after valid input
        }
       else {
          printf("not valid");/* repeat code in this else statement, maybe */
       }
   }while(1);
   system("pause");
}

若你们想停止程序，若用户输入了一个有效值，我的意思是1-15，那个么把这些for循环放到else块中，并添加break语句

do{
    printf("Input a value from 1 to 15: ");
    scanf("%d", &lines);

    //Check if inputed value is valid
    if(lines < 1 || lines > 15) {
        printf("Error: Please Enter a Valid number!!!\n");
        continue;
    }
    else{
    /*create triangle based on inputed value */
        for(a = 1; a <= lines; a++) {
            for(b=1; b<= a; b++) {
                printf("*");
            }
            printf("\n");
        }
        break;
   }
}while(1);
system("pause");
}

---

请给出一个无效值的示例。例如20，0x5，1000，abc。。。

do{
    printf("Input a value from 1 to 15: ");
    scanf("%d", &lines);

    //Check if inputed value is valid
    if(lines < 1 || lines > 15) {
        printf("Error: Please Enter a Valid number!!!\n");
        continue;
    }
    else{
    /*create triangle based on inputed value */
        for(a = 1; a <= lines; a++) {
            for(b=1; b<= a; b++) {
                printf("*");
            }
            printf("\n");
        }
        break;
   }
}while(1);
system("pause");
}