main函数命令行参数

#include <stdio.h>
#include <stdlib.h>

int main(int argc,char * argv[])
{
    int c,i,letter[26];
    FILE *ifp,*ofp;

    if(argc!=3){
        printf("\n%s%s%s\n\n%s\n%s\n\n",
               "Usage:",argv[0],"infile outfile",
               "in infile",
               "out file"
               );
         exit(1);
    }
    ifp=fopen(argv[1],"r");
    ofp=fopen(argv[2],"w");
    for(i=0;i<26;i++)
        letter[i]=0;
    while((c=getc(ifp))!=EOF)
        if(c>='A'&&c<='Z')
            ++letter[c-'A'];
    for(i=0;i<26;i++){
        if(i%6==0)
            putc('\n',ofp);
            fprintf(ofp,"%c:%5d     ",'A'+i,letter[i]);
    }
    putc('\n',ofp);
    return 0;
}

     用命令行cmd打开，然后到相应目录后，在该目录下对文件进行操作。