第6章循环9、计算一、二、三月还贷剩余金额，要求输入次数并显示剩余金额

    float loan, rate, payment;
    int n, i;
    printf("Enter amount of loan: ");
    scanf("%f", &loan);
    printf("rate: ");
    scanf("%f", &rate);
    printf("payment: ");
    scanf("%f", &payment);
    printf("time: ");
    scanf("%d", &n);
    rate = rate * 0.01 / 12;
    
    for(i=1; i <= n; i++){
        loan = loan + loan * rate - payment;
        printf("payment: $%.2f\n", loan);
    }