●说明: ◆if后面的表达式类型任意 ◆语旬可以是复合语旬 如:a=b&x printf( (a=b,X=y); (3 printf(OK 例考虑下面程序的输出结果: #include <stdio.h> main i int x,y; scant(“%d,%d”,&x,&y); if(x>y) V-X Compile error else x+;y++;} printf(“%d,%dn”,xy);
如：if(a==b&&x==y) printf(“a=b,x=y”); if(3) printf(“OK”); if(‘a’) printf(“%d”,’a’); ⚫说明： ◆if后面的表达式类型任意 ◆语句可以是复合语句 ◆ if(x) if(x!=0) if(!x) if(x==0) 例 考虑下面程序的输出结果: #include <stdio.h> main() { int x,y; scanf(“%d,%d”,&x,&y); if(x>y) x=y; y=x; else x++; y++; printf(“%d,%d\n”,x,y); } Compile Error!
例求一个数的绝对值 Include <stdio.h> mainO int x, y, printf( Enter an integer: ) scanf("od", &x); y-x, if(y<o y= -, printf(" integer: %od--->absolute value: %dn",x, y) 运行: Enter an integer:-12 integer: -12--->absolute value: 12
#include <stdio.h> main() { int x,y; printf("Enter an integer:"); scanf("%d",&x); y=x; if(y<0) y= -y; printf("\ninteger:%d--->absolute value:%d\n",x,y); } 例 求一个数的绝对值 运行：Enter an integer:-12 integer:-12--->absolute value :12
例输入两个数并判断两数相等否 ch42.c*/ Include <stdio. h> mainO int a b 运行: Enter integer a:12 printf("Enter integer a Enter integer b: 12+ scantron &a) a==b printf(" Enter integer b: scanf("d", &b) if(a-b) 运行: Enter integer a:12,J printf("a==bn") else Enter integer b: 9. printf("al=bn") al=b
/*ch4_2.c*/ #include <stdio.h> main() { int a,b; printf("Enter integer a:"); scanf("%d",&a); printf("Enter integer b:"); scanf("%d",&b); if(a==b) printf("a==b\n"); else printf("a!=b\n"); } 例 输入两个数并判断两数相等否 运行：Enter integer a:12 Enter integer b:12 a==b 运行：Enter integer a:12 Enter integer b:9 a!=b
例判断输入字符种类 #include <stdio. h> main( i char c printf("Enter a character c-getcharo if(c<0x20) printf("The character is a control character n") else if(c>=o'&&c<=9) printf("The character is a digit in") else if(c>='A'&&c<='z) printf("The character is a capital letterIn else if(c>='a'&&c=z) printf("The character is a lower letter n else printf("The character is other characterin") 运行: nter a character:F1 The character is other character
#include <stdio.h> main() { char c; printf("Enter a character:"); c=getchar(); if(c<0x20) printf("The character is a control character\n"); else if(c>='0'&&c<='9') printf("The character is a digit\n"); else if(c>='A'&&c<='Z') printf("The character is a capital letter\n"); else if(c>='a'&&c<='z') printf("The character is a lower letter\n"); else printf("The character is other character\n"); } 例 判断输入字符种类 运行：Enter a character： The character is a control character ：8 The character is a digit 运行： Enter a character： D The character is a capital letter 运行： Enter a character： h The character is a lower letter 运行： Enter a character：F1 The character is other character
☆i语旬嵌賽 般形式: if(expr1) if(expr1) if(expr2) if (expr2) 内嵌if statement statement1 内嵌if else ese statement statement2 if(expr1) statement1 if(expr1) if(expr2) statement, eise dIse f(expr3) statement2内嵌if else statement3内嵌if if(expr3) statements else statement statement4均嵌ir
❖if语句嵌套： ⚫一般形式： if (expr1) if (expr2) statement1 else statement2 else if(expr3) statement3 else statement4 内嵌if 内嵌if if (expr1) if (expr2) statement1 else statement2 内嵌if if (expr1) if (expr2) statement1 else statement3 内嵌if if (expr1) statement1 else if(expr3) statement3 else statement4 内嵌if