#include <iostream>
#include <stdio.h>
#include <string>
#include <sstream>
using namespace std;
string&   replace_all(string&   str, const   string&   old_value, const   string&   new_value)
{
	while (true)   {
		string::size_type   pos(0);
		if ((pos = str.find(old_value)) != string::npos)
			str.replace(pos, old_value.length(), new_value);
		else   break;
	}
	return   str;
}
int main()
{
	string begannum;
	string old_num;
	string new_num;
	printf("请输入你的字符串:");
	cin >> begannum;
	printf("请输入原来要替换的字符串:");
	cin >> old_num;
	printf("请输入要替换成的字符串:");
	cin >> new_num;
	cout << replace_all(begannum, old_num, new_num) << endl;
	while (1);
	return 0;
}

运行结果：

借鉴自：https://www.cnblogs.com/catgatp/p/6407783.html