每天学习一点编程（1）（输入一个表示整数的字符串，把该字符串转换成整数并输出）

输入一个表示整数的字符串，把该字符串转换成整数并输出。

/*输入一个表示整数的字符串，把该字符串转换成整数并输出。  例如：输入"345",输出345*/#include <iostream>#include <string>using namespace std;int calcu( char *s);int main(){char s[81];cout << "please enter the strings:" << endl;cin >> s;calcu(s);system("pause");return 0;}int calcu(char *s){int i;int val = 0;int len = strlen(s);if(s[0] == '+'){for(i = 1; i < len; i++)if(s[i] >= '0' && s[i] <= '9')val = val * 10 + s[i] - '0';elsebreak;if(i < len){    cout << "the input string is error." << endl;return -1;}}else if(s[0] == '-'){for(i = 1; i < len; i++)if(s[i] >= '0' && s[i] <= '9')val = val * 10 + s[i] - '0';else break;if(i < len){cout << "the input string is error." << endl;return -1;}val = -1 * val;}else if(s[0] >= '0' && s[0] <= '9'){for(i = 0; i < len; i ++){if(s[i] >= '0' && s[i] <= '9')val = val * 10 + s[i] - '0';else break;}if(i < len){cout << "the input string is error." << endl;return -1;}}else{cout << "the input string is error." <<endl;return -1;}cout << "the calculate number is: " << val <<endl;return 0;}