c - 这样当输入无效值时，用户必须在 C 中重试新值

Question

对于我的 HW 作业，我必须创建一个程序来输出一个基于星号的三角形，该三角形取决于用户输入。我已经让我的程序在用户输入整数时输出正确的三角形，但我的问题是当输入无效值时如何使用户必须重新尝试提交值？我查看了论坛，但找不到类似的问题。

#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");
}

Answer 1

#include <stdio.h>

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

//prompt user to input integer
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;
    }
    /*create triangle based on inputed value */
        for(a = 1; a <= lines; a++) {
            for(b=1; b<= a; b++) {
                printf("*");
            }
            printf("\n");
        }
}while(1);
system("pause");
}

如果你想在用户输入有效值(我的意思是 1-15)时停止程序，那么将这些 for 循环放在 else block 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");
}