5-1#include"stdio.h"voidmain(){charc1,c2;printf("c1:");c1=getchar();if(c1>='a'&&c1<='z')c2=c1-32;elseif(c1>='A'&&c1<='Z')c2=c1+32;elsec2=c1;printf("=>%c\n",c2);}5-2#include"stdio.h"voidmain(){charc;printf("c:");c=getchar();if(c>='A'&&c<='Z')if(c=='A')printf("没有前面的字母！");elseif(c=='Z')printf("没有后面的字母!!");elseprintf("前面的字母=%c,后面的字母=%c",c-1,c+1);printf("\n");}5-3#include"stdio.h"voidmain(){ints;charg;printf("s:");scanf("%d",&s);if(s>=0&&s<=100){switch(s/10){case9:case10:g='A';break;case8:g='B';break;case7:g='C';break;case6:g='D';break;default:g='E';}printf("g=%c\n",g);}elseprintf("成绩不在百分制范围内！\n");}5-4#include"stdio.h"voidmain(){inty,m,d,dok;intyy,mm,dd;printf("y,m,d:");scanf("%d,%d,%d",&y,&m,&d);switch(m){case1:case3:case5:case7:case8:case10:case12:if(d>0&&d<=31)dok=4;elsedok=0;break;case4:case6:case9:case11:if(d>0&&d<=30)dok=3;elsedok=0;break;case2:if(y%4==0&&y%100!=0||y%400==0)if(d>0&&d<=29)dok=2;elsedok=0;elseif(d>0&&d<=28)dok=1;elsedok=0;break;default:dok=0;}if(dok==0)printf("月份或日期不对！\n");else{switch(dok){case1:if(d==28){yy=y;dd=1;mm=m+1;}else{yy=y;dd=d+1;mm=m;}break;case2:if(d==29){yy=y;dd=1;mm=m+1;}else{yy=y;dd=d+1;mm=m;}break;case3:if(d==30){yy=y;dd=1;mm=m+1;}else{yy=y;dd=d+1;mm=m;}break;case4:if(d==31)if(m==12){yy=y+1;dd=1;mm=1;}else{yy=y;dd=1;mm=m+1;}else{yy=y;dd=d+1;mm=m;}break;}printf("Tomorrow:%d年%d月%d日\n",yy,mm,dd);}}5-5#include"stdio.h"voidmain(){inta,b,c,t;printf("a,b,c:");scanf("%d,%d,%d",&a,&b,&c);if(a+b>c&&b+c>a&&a+c>b){if(a>b){t=a;a=b;b=t;}if(a>c){t=a;a=c;c=t;}if(b>c){t=b;b=c;c=t;}if(a==b&&b==c)printf("等边三角形.");elseif(a==b||b==c||a==c)printf("等腰角形.");elseif(c*c==a*a+b*b)printf("直角三角形.");elseprintf("任意三角形.");printf("\n");}elseprintf("