C Primer Plus 第6章 C控制语句：循环 编程练习

记录下写的最后几题。

14.
#include <stdio.h>

int main() {
    double value[8];
    double value2[8];
    int index;
    for (index = 0; index < 8; ++index) { //输入值。
        printf("value #%d:", index + 1);
        scanf("%lf", &value[index]);
    }

    for (index = 0; index < 8; index++) {
        printf("%10.2lf", value[index]);
    }
    printf("\n");

    value2[0] = value[0];
    for (index = 1; index < 8; ++index) {
        value2[index] = value2[index - 1] + value[index];
    }
    for (index = 0; index < 8; index++) {
        printf("%10.2lf", value2[index]);
    }
    return 0;
}

15.
#include <stdio.h>

int main() {
    char symbol[255], ch;
    int i = 0;

    do {
        scanf("%c", &ch);
        symbol[i++] = ch;
    } while (ch != '\n');

    while (i >= 0) {
        printf("%c", symbol[i - 2]);
        // -2是因为减去\n和最后多出来的一个没用的i，大概就是这个意思吧。
        i--;
    }
    return 0;
}

16.
#include <stdio.h>

#define PRINCIPAL 100.0
#define RATE_DAPHNE 0.1
#define RATE_DEIRDRE 0.05

// 给出本金，利率。
int main() {
    double Daphne = PRINCIPAL;
    double Deirdre = PRINCIPAL;
    int years = 0;
    while (Daphne >= Deirdre) {
        Daphne = Daphne + RATE_DAPHNE * PRINCIPAL;
        Deirdre = Deirdre + Deirdre * RATE_DEIRDRE;
        years++;
    }
    printf("Daphone:$%.2lf \nDeirdre:$%.2lf \n", Daphne, Deirdre);
    printf("Investment values after %d years.", years);
    return 0;
}

17.
#include <stdio.h>

#define RATE 0.08

// 给出利率。
int main() {
    double principal = 100.0;
    int years = 0;
    while (principal > 0) {
        principal = principal + principal * RATE - 10;
        years++;
    }
    printf("It takes %d years to complete.", years);
    return 0;
}

18.
#include <stdio.h>

#define DUNBARS_NUMBER 150

int main() {
    int friend = 5;
    int value = 1;
    int week = 1;
    while (DUNBARS_NUMBER > friend) {
        friend = (friend - value) * 2;
        value++;
        printf("Rabnud have %3d friends on the %2d of the week. \n",
               friend, week);
        week++;
    }
    return 0;
}