C-00001-字符处理

#include<stdio.h> 
#include<stdlib.h> 
#include<string.h> 
#define MAX_COLS 20 
#define MAX_INPUT 1000 

int read_column_numbers(int columns[],int max); 
void rearrange(char *output,char const *input,int n_columns,int const columns[]); 

int main(void) 
{ 
    int n_columns; 
    int columns[MAX_COLS]; 
    char input[MAX_INPUT]; 
    char output[MAX_INPUT]; 

n_columns = read_column_numbers(columns,MAX_COLS); 

while(gets(input) != NULL) 
{ 
    printf("Original input:%s\n",input); 
    rearrange(output,input,n_columns,columns); 
    printf("Rearranged line:%s\n",output); 
} 
    return EXIT_SUCCESS; 
} 
    int read_column_numbers(int columns[],int max) 
{ 
    int num = 0; 
    int ch; 
    while(num<max && scanf("%d",&columns[num]) ==1 && columns[num] >= 0) 
    num += 1; 
    if(num % 2 != 0) 
    { 
        puts("Last column number is not paired."); 
        exit(EXIT_FAILURE); 
    } 
    while((ch = getchar())!=EOF && ch != '\n') 
    ; 
} 
void rearrange(char *output,char const *input,int n_columns,int const columns[]) 
{ 
    int col; 
    int output_col; 
    int len; 

    len = strlen(input); 
    output_col = 0; 

    for(col = 0; col < n_columns ;col += 2) 
    { 
        int nchars = columns[col+1] - columns[col] + 1; 
        if(columns[col] >= len || output_col == MAX_INPUT -1) 
            break; 
        if(output_col + nchars > MAX_INPUT -1) 
        nchars = MAX_INPUT - output_col -1; 
        strncpy(output + output_col,input + columns[col],nchars); 
         output_col += nchars; 
    } 
     output[output_col] = '\0'; 
}