第三章

3-1

#include<stdio.h>
int main(void)
{
    int  mynumber=38;
    int  yournumber;

    printf("Input your number:");
    scanf("%d",&yournumber);
    if(yournumber==mynumber)
        printf("Ok!you are right!
");
    else
        if(yournumber>mynumber)
            printf("Sorry!your number is bigger than my number!
");
        else
            printf("Sorry!your number is smaller than my number!
");

    return 0;
}

3-2

#include<stdio.h>
int main(void)
{
    int number;


    printf("Enter a number:");
    scanf("%d",&number);
    if(number%2==0){
        printf("The number is even.
");
    }
    else{
        printf("The number is odd.
");
    }

    return 0;
}

3-3

#include<stdio.h>
int main(void)
{
    int count,i,n;
    double grade,total;

    printf("Enter n:");
    scanf("%d",&n);
    total=0;
    count=0;
    for(i=1;i<=n;i++){
        printf("Enter  grade#%d:",i);
        scanf("%lf",&grade);
        total=total+grade;
        if(grade<60){
            count++;
        }
    }
    printf("Grade average=%.2f
",total/n);
    printf("Number of failures=%d
",count);
    
    return 0;
}

3-4

#include<stdio.h>
int main(void)
{
    double x,y;


    printf("Enter x:");
    scanf("%lf",&x);
    if(x<0){
        y=0;
    }
    else if(x<=15){
        y=4*x/3;
    }
    else{
        y=2.5*x-10.5;
    }

    printf("f(%.2f)=%.2f
",x,y);

    return 0;
}

3-5

#include<stdio.h>
int main(void)
{
    double value1,value2;
    char op;

    printf("Type in an expression:");
    scanf("%lf%c%lf",&value1,&op,&value2);

    if(op=='+')
        printf("=%.2f
",value1+value2);
    else if(op=='-')
        printf("=%.2f
",value1-value2);
    else if(op=='*')
        printf("=%.2f
",value1*value2);
    else if(op=='/')
        printf("=%.2f
",value1/value2);
    else
        printf("Unknown operator
");

    return 0;
}

3-7

#include<stdio.h>
int main(void)
{
    int digit,letter,other;
    char ch;
    int i;
    digit=letter=other=0;
    printf("Enter 10 characters:");
    for(i=1;i<=10;i++){
        ch=getchar();
        if((ch>='a'&&ch<='z')||(ch>='A'&&ch<='Z'))
            letter++;
        else if(ch>='0'&&ch<='9')
            digit++;
        else
            other++;
    }
    printf("letter=%d,digit=%d,other=%d
",letter,digit,other);

    return 0;
}

3-8

#include<stdio.h>
int main(void)
{
    int choice,i;
    double price;

    for(i=1;i<=5;i++){
        printf("[1]Select crisps 
");
        printf("[2]Select popcorn 
");
        printf("[3]Select chocolate 
");
        printf("[4]Select cola 
");
        printf("[0]exit 
");

        printf("Enter choice:");
        scanf("%d",&choice);

        if(choice==0)
            break;
        switch(choice){
            case 1:price=3.0;break;
            case 2:price=2.5;break;
            case 3:price=4.0;break;
            case 4:price=3.5;break;
            default:price=0.0;break;
        }
        printf("price=%0.1f
",price);
    }
      printf("Thanks 
");

      return 0;
}

3-9

#include<stdio.h>
int main(void)
{
    double value1,value2;
    char op;

    printf("Type in an expression:");
    scanf("%lf%c%lf",&value1,&op,&value2);
    switch(op){
    case'+':
        printf("=%.2f
",value1+value2);
        break;
    case'-':
        printf("=%.2f
",value1-value2);
        break;
    case'*':
        printf("=%.2f
",value1*value2);
        break;
    case'/':
        printf("=%.2f
",value1/value2);
        break;
    }

    return 0;
}

3-10

#include<stdio.h>
int main(void)
{
    int blank,digit,other;
    char ch;
    int i;
    blank=digit=other=0;
    printf("Enter 10 characters:");
    for(i=1;i<=10;i++){
        ch=getchar();
        switch(ch){
         case' ':
         case'
':
             blank++;
             break;
         case'0':case'1':case'2':case'3':case'4':
         case'5':case'6':case'7':case'8':case'9':
             digit++;
             break;
         default:
             other++;
             break;
        }
    }
    printf("blank=%d,digit=%d,other=%d
",blank,digit,other);

    return 0;
}

3-11

#include<stdio.h>
int main(void)
{
    double value1,value2;
    char op;

    printf("Type in an expression:");
    scanf("%lf%c%lf",&value1,&op,&value2);
    if(op=='+')
        printf("=%.2f
",value1+value2);
    else if(op=='-')
        printf("=%.2f
",value1-value2);
    else if(op=='*')
        printf("=%.2f
",value1*value2);
    else if(op=='/')
        if(value2!=0)
            printf("=%.2f
",value1/value2);
        else
            printf("Divisor can not be 0!
");
    else
        printf("Unknown operator!
");

    return 0;
}