字符串转换为整数

#include <stdio.h>int check(char *s){char *p;p = s;if((s[0] != '+') || (s[0] != '-') ||(*p > '9') ||(*p < '0')){}else{return 0;}while(*(++p) != '/0'){if((*p > '9') || (*p < '0')){return 0;}}return 1;}long f(char *p){long i = 1;long k = 0;long t = 10;if(!check(p)){puts("data error/n");exit();}for( ; ; ){k += (p[i]-'0');i++;if(p[i] == '/0'){break;}k *= 10;t *= 10;}if(p[0] == '-'){return (-1*k);}else if(p[0] == '+'){return (k);}else{k += (p[0]-'0')*t;return (k);}}int main(){char a[10];long i;clrscr();scanf("%s",a);i = f(a);printf("/n%ld",i);return 0;}