利用C語言實現輸入年月日計算當年天數

閒來無事，重學c語言

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

void main(){
    int a,b,c,d;
    printf("pls input year/m/d:\n");
    scanf("%d %d %d",&a,&b,&c);
    switch (b) {
        case 1:
            printf("is %ddays\n",c);
            break;
    }
    if(((a%4==0&&a%100!=0)||(a%400==0))&&(2<b||2==b)){
        switch (b) {
            case 2:
                printf("is %ddays\n",d=31+c);break;
            case 3:
                printf("is %ddays\n",d=60+c);break;
            case 4:
                printf("is %ddays\n",d=91+c);break;
            case 5:
                printf("is %ddays\n",d=121+c);break;
            case 6:
                printf("is %ddays\n",d=152+c);break;
            case 7:
                printf("is %ddays\n",d=182+c);break;
            case 8:
                printf("is %ddays\n",d=213+c);break;
            case 9:
                printf("is %ddays\n",d=244+c);break;
            case 10:
                printf("is %ddays\n",d=274+c);break;
            case 11:
                printf("is %ddays\n",d=305+c);break;
            case 12:
                printf("is %ddays\n",d=335+c);break;
            break;
        }
    }else{
        switch (b) {
            case 2:
                printf("is %ddays\n",d=31+c);break;
            case 3:
                printf("is %ddays\n",d=59+c);break;
            case 4:
                printf("is %ddays\n",d=90+c);break;
            case 5:
                printf("is %ddays\n",d=120+c);break;
            case 6:
                printf("is %ddays\n",d=151+c);break;
            case 7:
                printf("is %ddays\n",d=181+c);break;
            case 8:
                printf("is %ddays\n",d=212+c);break;
            case 9:
                printf("is %ddays\n",d=243+c);break;
            case 10:
                printf("is %ddays\n",d=273+c);break;
            case 11:
                printf("is %ddays\n",d=304+c);break;
            case 12:
                printf("is %ddays\n",d=334+c);
                break;
        }
    }
}

注意：一定要考慮輸入年份是否爲閏年且月份是否大於2.