关于Ubuntu Linux系统下使用C的有关问题

      1        // P95: 2.编程题 (6)调用库函数编程求表达式cos(39.5度)+(e的2.916次幂)+(3.16的算数方根)
      2    
      3     // The begining of C program: test03-06.c.
      4    
      5    // Header files included.
      6    #include <stdio.h>
      7    #include <math.h>
      8
      9    // Macro definition.
    10    #define PI 3.1415926
    11    
    12    // Main function's declaration.
    13    int  main ( void )
    14    {
    15          long int  temp=0;
    16          float     result=0.0;
    17          result = cos(39.5*PI/180) + exp(2.916) + sqrt(3.16);
    18          temp = (long int) (result * 100);
    19          temp = (long int) ((result*100 - temp)*2 + temp);
    20          result = temp / 100.0;
    21          printf ( "Result: cos(39.5*PI/180) + exp(2.916) + sqrt(3.16) = %.2lf\n",
    22                       result );
    23        
    24          return  (0);
    25    }
    26    
    27    // The end of C program: test03-06.c.
    28    

      1    // P120: 3.编程题 (3)
      2    
      3    // The begining of C program: test04-03.c.
      4    
      5    // Header files included.
      6    #include <stdio.h>
      7    #include <math.h>
      8    
      9    // Main function's declaration.
    10    int  main ( void )
    11    {
    12          long int  i_tag=0;
    13          float     f_num1,  f_num2,  f_num3;
    14          double    area=0.0,  temp=0.0;
    15          printf ( "Input the three side's length of triangle: " );
    16          scanf  ( "%f %f %f", &f_num1, &f_num2, &f_num3 );
    17          if ( (f_num1<=0) || (f_num2<=0) || (f_num3<=0) )
    18          {
    19                printf ( "Input error, data is illegal!\n" );
    20                return  (1);
    21          }
    22          if ( ((fabs(f_num2-f_num3) < f_num1) && (f_num1 < (f_num2+f_num3))) ||
    23               ((fabs(f_num1-f_num3) < f_num2) && (f_num2 < (f_num1+f_num3))) ||
    24               ((fabs(f_num1-f_num2) < f_num3) && (f_num3 < (f_num1+f_num2))) )
    25          {
    26                printf ( "The three sides can form a triangle.\n" );
    27                temp = ( f_num1 + f_num2 + f_num3 ) / 2;
    28                area = temp*fabs(f_num1-temp)*fabs(f_num2-temp)*fabs(f_num3-temp);
    29                area = sqrt(area);
    30            
    31                // 对所求结果四舍五入并保留到小数点后两位之后输出
    32                i_tag = (long int) (area * 100);
    33                i_tag = (long int) ((area*100 - i_tag)*2 + i_tag);
    34                area = i_tag / 100.0;
    35                printf ( "The triangle's area is: %-.2lf\n", area );
    36            
    37                return  (0);
    38          }
    39          else
    40                printf ( "The three sides can't form a triangle.\n" );
    41        
    42          return  (0);
    43    }
    44    
    45    // The end of C program: eg04-03.c.
    46