C--3 (Array, Function

Array

#include<stdio.h>int main(){   int c,i,nwhite,nother;   int ndigit[10];   nwhite = nother = 0;   for(i=0;i<10;++i)      ndigit[i]=0;   while( (c=getchar())  != 'Q')       if (c>='0'  &&  c<='9')          ++ndigit[c-'0'];       else  if ( c ==' ' || c =='\n' || c=='\t')                ++nwhite;       else                 ++nother;   printf("digits =");   for(i=0;i<10;++i)       printf(" %d",ndigit[i]);   printf(", white space = %d, other = %d\n",nwhite,nother);}

The declaration:

int ndigit[10];

定义了从ndigit[0]…ndigit[9],
A subscript can be any integer expression,whici includes integer variables like i, and integer constants.

C-'0'

This works only if ‘0’,’1’…’9’; an integer expression;

Function

• 等用subroutine
• Encapsulating some computation

  return-type function-name ( parameter declarations, if any)  { declarations  statements }

• For example:

int power( int base, int n){   statements  }

• 上例中，{ }内的参数名，只适用本例，与main 函数中同名的参数不相关
• The value that power computes is returned to main by the return statement.

return expression;

• There is a return statement at the end of main. Since main is a function like any other, it may return a value to its caller..
• A return value of zero implies normal termination; non-zero values signal unusual or erroneous termination conditions.
• We have omitted return statements from our main function up to this point, but we will include them hereafter, as a reminder that programs should return status to their environment.

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int power(int  ,  int  );

• just before main says that power is a function that expects two int arguments and returns an int. Called a function prototype.