在上一篇博文中介绍了如何实现将整数转换为字符串，这里在介绍一个将字符串转换为整数的实现方法。
1 #include <stdio.h> 2 #include <stdlib.h> 3 4 int isspace(int x); 5 int isspace(int x); 6 int my_atoi(const char *nptr); 7 8 int main(void) 9 { 10 char str[33]; 11 int num; 12 scanf("%s", str); 13 num = my_atoi(str); 14 printf("Ans: %d ", num); 15 16 return 0; 17 } 18 19 int isspace(int x) 20 { 21 if(x==' ' || x==' ' || x==' ' || x=='f' || x=='' || x==' ') 22 return 1; 23 else 24 return 0; 25 } 26 27 int isdigit(int x) 28 { 29 if(x<='9' && x>='0') 30 return 1; 31 else 32 return 0; 33 } 34 35 int my_atoi(const char *nptr) 36 { 37 int c; /* current char */ 38 int total; /* current total */ 39 int sign; /* if '-', then negative, otherwise positive */ 40 41 /* skip whitespace */ 42 while ( isspace((int)(unsigned char)*nptr) ) 43 ++nptr; 44 45 // 读取第一个非空白符 46 c = (int)(unsigned char)*nptr++; 47 sign = c; /* save sign indication */ 48 if (c == '-' || c == '+') 49 c = (int)(unsigned char)*nptr++; /* skip sign */ 50 51 total = 0; 52 53 while (isdigit(c)) { 54 total = 10 * total + (c - '0'); /* accumulate digit */ 55 c = (int)(unsigned char)*nptr++; /* get next char */ 56 } 57 58 if (sign == '-') 59 return -total; 60 else 61 return total; /* return result, negated if necessary */ 62 }