プログラマ専用SNS ミクプラ

#include <stdio.h>


/******************************************/
void ym_input(int *year, int *month);

int get_day_of_week(char *date);

void cal_disp(int year,int month, int dayofweek);


/******************************************/
char *dp,date[8] = {0,0,0,0,0,0,0,0};
int *yp, *mp;
int year,month,day,dayofweek;


/******************************************/
int main(void)
{
	yp = date[0];
	mp = date[4];
	ym_input(yp,mp);

	date[6] = '0';
	date[7] = '1';
	dp = date[0];
	dayofweek = get_day_of_week(dp);

	cal_disp(year,month,dayofweek);

	return 0;
}


/******************************************/
void ym_input(int *year, int *month)
{
	printf("表示させたいカレンダーの年を西暦で入力してください\nただし入力可能範囲は1583～3999年とする ->");
	while('15830000'>=date || '39990000'<=date){
		scanf("%d",&year);
		if('15830000'>=date || '39990000'<=date)	printf("Error:入力値が正しくありません\n");
	}
	printf("表示させたいカレンダーの月を入力してください ->");
	while('0100'>=*month || '1200'<=*month){
		scanf("%d",&month);
		if('0100'>=*month || '1200'<=*month)	printf("Error:入力値が正しくありません\n");
	}
}


/******************************************/
int get_day_of_week(char *date)
{
	int i,d[8],a;
	int *j;

	j = d[0];
	for(i=0;i<8;i++)
	{
		*(j + i) = *(date + i) - 48;
	}

	year = d[0] * 1000 + d[1] * 100 + d[2] * 10 + d[3];
	month = d[4] * 10 + d[5];
	day = d[6] * 10 + d[7];

	a=(year+(year/4)-(year/100)+(year/400) + ((13 * month)+8)/5)+day)%7 ;
	return a;
}


/******************************************/
void cal_disp(int year,int month, int dayofweek)
{
	int i,j,a,max,flag,cal[6][7]={
		{" "," "," "," "," "," "," "},
		{" "," "," "," "," "," "," "},
		{" "," "," "," "," "," "," "},
		{" "," "," "," "," "," "," "},
		{" "," "," "," "," "," "," "},
		{" "," "," "," "," "," "," "}
	};

	switch(month){
		case 2 : {
			if((year%4==0&&!(year%100==0))||year%400==0)
				max=29;
			else
				max=28;
			break;
				 }
		case 4 :
		case 6 :
		case 9 :
		case 11 : {
			max=30;
			break;
				  }
		default : {
			max=31;
			break;
				  }
	}

	a=0;
	flag=0;
	for(i=0;i<6||flag==1;i++){
		for(j=0;j<7||flag==1;j++){
			if(i=0)	j=dayofweek;
			cal[j]=a++;
			if(a==max) flag=1;
		}
	}
	printf("%.4d年 %.2d月\n",year,month);
	printf("日　月　火　水　木　金　土\n");

	for(i=0;i<6||flag==1;i++){
		for(j=0;j<7||flag==1;j++){
			if(cal[j]=" ")
				printf("　");
			else
				printf("%.2d",cal[j]);
			printf("　");
		}
		printf("\n");
	}

}

そこよりも前に、main()で警告が出ていませんか？

>	yp = date[0];
>	mp = date[4];

date[0]やdate[4]というchar型のデータ(中身は0、つまり'\0')を
int *型に代入する意味がわからないです。

cal_disp()の例を載せます。
他の関数のコードは考えてみてください。


void cal_disp(int year, int month, int dayofweek)
{
	int days[2][13] = {
		{ 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },		// 平年
		{ 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 },		// 閏年
	};
	int leap, lastday, w, d, n;
	
	leap = year % 4 == 0 && year % 100 != 0 || year % 400 == 0;		// 閏年の判定
	lastday = days[leap][month];			// 当該月の日数
	
	printf("\n%d年%2d月\n", year, month);
	printf("日 月 火 水 木 金 土\n");
	for (w = 0; w < 6; w++) {				// 1ヶ月を6週とする
		n = 7 * w + 1 - dayofweek;			// 第w週日曜日の日付
		for (d = n; d < n + 7; d++) {		// 第w週を出力する
			if (1 <= d && d <= lastday)		// 有効な日付ならば
				printf("%2d ", d);			// 出力する
			else							// 無効な日付ならば
				printf("   ");				// 空白を出力する
		}
		printf("\n");
	}
	printf("\n");
}