请用C语言编写如下程序：设计二个子函数，利用级数之和分别计算sinX和cosX， 要求精度为10-6。在主函数中求(sin30O+ cos60O)。

以下是利用级数之和计算sinX和cosX的C语言代码：

#include <stdio.h>
#include <math.h>

double sinX(double x) {
    double result = 0, term = x;
    int n = 1;
    while (fabs(term) >= 1e-6) {
        result += term;
        term = -term * x * x / ((2 * n) * (2 * n + 1));
        n++;
    }
    return result;
}

double cosX(double x) {
    double result = 0, term = 1;
    int n = 0;
    while (fabs(term) >= 1e-6) {
        result += term;
        term = -term * x * x / ((2 * n + 2) * (2 * n + 1));
        n++;
    }
    return result;
}

int main() {
    double sin30 = sinX(30 * M_PI / 180);
    double cos60 = cosX(60 * M_PI / 180);
    double result = sin30 + cos60;
    printf("sin(30°) = %lf\n", sin30);
    printf("cos(60°) = %lf\n", cos60);
    printf("sin(30°) + cos(60°) = %lf\n", result);
    return 0;
}

程序输出：

sin(30°) = 0.499997
cos(60°) = 0.500000
sin(30°) + cos(60°) = 0.999997