这个程序功能很简单，但具体要求非常多。考虑到程序的严谨性所以要针对所有可能出现的情况进行处理。第一次进行test cases测试的时候一大半的test cases都没有通过，进行分析修改后以下程序通过所有的test cases. 因为限制只能用部分C的function,所以要求较高的逻辑思维能力。
这个程序看似很难看，用了很多个相套的if statement.
如果需要具体的程序说明文档和test cases请与我联系。
#include <stdio.h>#include <limits.h>
/* Specify the priority of error message */
#define INVALID_SYNTAX 5;#define OVERFLOW 4;#define IMPOSSIBLE_TIME 3;#define END_BEFORE_START 2;#define AMBIGUOUS 1;int main(void){
int c; /* read a character one by one and save it into c */
int length; /* length of the number */ char s[1000]; /* the string used to save the input number */ unsigned long long start_time, end_time; /* variables used to store the atart time and end time */ int message_number; /* store the defined message number, decide which message should be displayed */ int first_ambi, second_ambi; /* check if the first and second numbers are ambiguous */
while((c = getchar()) != EOF) { length = 0; /************************/ start_time = 0; /* */ end_time = 0; /* initialize variables */ message_number = 0; /* */ first_ambi = 1; /* */ second_ambi = 1; /************************/ while(c == ' ' || c == '\t' || c == '\0') c = getchar(); /* remove the leading space, tab or \0 */ /* if the first input character is a digit */ if(c == '0' || c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7' || c == '8' || c == '9') { s[length] = c; length++; int check = 1; /* get the first input number */ while(check != 0 && (c = getchar()) != EOF) { if(c == '0' || c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7' || c == '8' || c == '9') { s[length] = c; length++;
} else check = 0; } int i; /* convert the string to a decimal number */ for(i = 0; i < length; i++) { unsigned long long temp_number = s[i] - 48; if(i == length - 1) start_time = start_time + s[i] - 48; else { int x; for(x = i; x < length - 1; x++) temp_number = temp_number * 10; start_time = temp_number + start_time; } } /* check if the number overflow */ if(start_time > UINT_MAX) { if(message_number < 4) message_number = OVERFLOW; } /* If the number ends with white space, which means no "am" or "pm". We have to check if the number is from 0 to 23 */ if(c == ' ' || c == '\t' || c == '\0') { if(start_time != 0 && start_time <= 12) first_ambi = 0; if(start_time > 24) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } if(start_time == 12) start_time = 0; /*12 can be 12am and 12pm, now we let start_time be 12am */ } /* when the number ends with "am" */ else if(c == 'a') { if((c = getchar()) == 'm') { /* check if the number which ends with "am" is greater than 12 or equals to 0 */ if(start_time > 12 || start_time == 0) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } /* 12am means midnight */ if(start_time == 12) start_time = 0; } else message_number = INVALID_SYNTAX; } /* when the number ends with "pm" */ else if(c == 'p') { if((c = getchar()) == 'm') { /* check if the number which ends with "pm" is greater than 12 or equals to 0 */ if(start_time > 12 || start_time == 0) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } /* 12pm means noon */ else if(start_time == 12) ; else start_time = start_time + 12; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } /* if the first input character is 'n', we want to check if it is followed by "oon" */ else if(c == 'n') { if((c = getchar()) == 'o') { if((c = getchar()) == 'o') { if((c = getchar()) == 'n') { if((c = getchar()) == '\0' || c == ' ' || c == '\t') /* the end of string "noon" */ { start_time = 12; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } /* if the first input character is 'm', we want to check if it is followed by "idnight" */ else if(c == 'm') { if((c = getchar()) == 'i') { if((c = getchar()) == 'd') { if((c = getchar()) == 'n') { if((c = getchar()) == 'i') { if((c = getchar()) == 'g') { if((c = getchar()) == 'h') { if((c = getchar()) == 't') { if((c = getchar()) == '\0' || c == ' ' || c == '\t') /* the end of string "midnight" */ { start_time = 0; first_ambi = 1; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; length = 0; /* initialize variable */ if(c != '\n') { /* check if there is no white space after the start time */ if((c == 'm'||c == 't'||c == 'n') && (c = getchar()) != ' ' && c != '\t' && c != '\0') message_number = INVALID_SYNTAX; /* remove the white space after the start time */ while(c == ' ' || c == '\t' || c == '\0') c = getchar(); } /* if the second input character is a digit */ if(c == '0' || c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7' || c == '8' || c == '9') { s[length] = c; length++; int check = 1; /* get the second input number */ while(check != 0 && (c = getchar()) != EOF) { if(c == '0' || c == '1' || c == '2' || c == '3' || c == '4' || c == '5' || c == '6' || c == '7' || c == '8' || c == '9') { s[length] = c; length++; } else check = 0; } int i; /* convert the string to a decimal number */ for(i = 0; i < length; i++) { unsigned long long temp_number = s[i] - 48; if(i == length - 1) end_time = end_time + s[i] - 48; else { int x; for(x = i; x < length - 1; x++) temp_number = temp_number * 10; end_time = temp_number + end_time; } } /* check if the number overflow */ if(end_time > UINT_MAX) { if(message_number < 4) message_number = OVERFLOW; } /* If the number ends with white space, which means no "am" or "pm". We have to check if the number is from 0 to 23 */ if(c == ' ' || c == '\t' || c == '\n' || c == '\0') { if(end_time <= 12) second_ambi = 0; if(end_time > 24) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } } /* when the number ends with "am" */ else if(c == 'a') { if((c = getchar()) == 'm') { /* check if the number which ends with "am" is greater than 12 or equals to 0 */ if(end_time > 12 || end_time == 0) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } /* 12am means midnight */ if(end_time == 12) { end_time = 24; second_ambi = 0; } } else message_number = INVALID_SYNTAX; } /* when the number ends with "pm" */ else if(c == 'p') { if((c = getchar()) == 'm') { /* check if the number which ends with "pm" is greater than 12 or equals to 0 */ if(end_time > 12 || end_time == 0) { if(message_number < 3) message_number = IMPOSSIBLE_TIME; } /* 12pm means noon */ else if(end_time == 12) ; else end_time = end_time + 12; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } /* if the first input character is 'n', we want to check if it is followed by "oon" */ else if(c == 'n') { if((c = getchar()) == 'o') { if((c = getchar()) == 'o') { if((c = getchar()) == 'n') { if((c = getchar()) == '\0' || c == ' ' || c == '\t' || c == '\n') /* the end of string "noon" */ { end_time = 12; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } /* if the first input character is 'm', we want to check if it is followed by "idnight" */ else if(c == 'm') { if((c = getchar()) == 'i') { if((c = getchar()) == 'd') { if((c = getchar()) == 'n') { if((c = getchar()) == 'i') { if((c = getchar()) == 'g') { if((c = getchar()) == 'h') { if((c = getchar()) == 't') { if((c = getchar()) == '\0' || c == ' ' || c == '\t' || c == '\n') /* the end of string "midnight" */ { end_time = 24; second_ambi = 0; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; } else message_number = INVALID_SYNTAX; /* if the two times are definite, we do not have to check if they are ambiguous. Just check if the time end before start*/ if((first_ambi == 1 || start_time > 12) && (second_ambi == 1 || (end_time > 12 && end_time != 24))) { if(end_time < start_time && message_number < 2) message_number = END_BEFORE_START; } /* if the first time is definite but the second time is ambiguous, the time interval may be ambiguous */ else if((first_ambi == 1 || start_time >= 12) && (second_ambi == 0 && (end_time <= 12 || end_time == 24))) { if(start_time == 0 && (end_time == 0 || end_time == 24) && message_number < 1) message_number = AMBIGUOUS; if((start_time < end_time) && end_time != 24) { if(message_number < 1) message_number = AMBIGUOUS; } else { if(end_time <= 12) end_time = end_time + 12; if(end_time < start_time && message_number < 2) message_number = END_BEFORE_START; } } /* if the first time is ambiguous but the second time is definite, the time interval may be ambiguous */ else if((first_ambi == 0 && start_time <= 12) && (second_ambi == 1 || end_time > 12)) { if(start_time + 12 < end_time) { if(message_number < 1) message_number = AMBIGUOUS; } if(end_time < start_time && message_number < 2) message_number = END_BEFORE_START; } /* When the two times are both ambiguous, we have to check if there is only one pair of times that can be calculated */ else if((first_ambi == 0 && start_time <= 12) && (second_ambi == 0 && (end_time <= 12 || end_time == 24))) { if(start_time == 0 && (end_time == 0 || end_time == 24) && message_number < 1) message_number = AMBIGUOUS; if(start_time >= end_time) end_time = end_time + 12; /* if end_time + 12, then end_time must be greater than start_time */ else if((start_time < end_time) && message_number < 1) message_number = AMBIGUOUS; } /* if the input time ends with 'm', read one more character */ if(c == 'm') c = getchar(); while(c != '\n') { /* when the input contains something else except the white space after the second time, print error message*/ if(c != '\t' && c != ' ' && c != '\0') message_number = INVALID_SYNTAX; c = getchar(); } /* One message should be print. That depends on the specified priority */ if(message_number == 5) printf("invalid syntax\n"); else if(message_number == 4) printf("overflow\n"); else if(message_number == 3) printf("impossible time\n"); else if(message_number == 2) printf("end before start\n"); else if(message_number == 1) printf("ambiguous\n"); else printf("%d\n", end_time - start_time); /* printf the number of hours worked */ } return 0;
}
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