一個文字串可用事先給定的字母對映表進行加密。例如，假設字母對映表為：

a b c d e f g h i j k l m n o p q r s t u v w x y z
n g z q t c o b m u h e l k p d a w x f y i v r s j
則字串“encrypt”被加密為“tkzwsdf” 要求：設計程式將輸入的文字串進行加密後輸出，然後進行解密並輸出。

//main.cpp
#include <iostream>
#include "SqString.h"
using namespace std;

SqString sqStr,
 
 matchStr;	//這兩個變數在main函式中作初始化

int main()
{
	SqString encrypt(SqString p);			//函式宣告
	SqString Unencrypt(SqString q);			//函式宣告
	SqString p, q;
	char inputStr[MaxSize];					//存放輸入的字串
	char sqChar[MaxSize] = "abcdefghijklmnopqrstuvwxyz";		//順序字串
	char matchChar[MaxSize] = "ngzqtcobmuhelkpdawxfyivrsj";		//對映字串
	strAssign
 
(sqStr, sqChar);
	strAssign(matchStr, matchChar);
	cout << "請輸入要加密的字串：" << endl;
	cin >> inputStr;
	strAssign(p, inputStr);
	cout << "你輸入的字串為:" << endl;
	DispStr(p);
	q = encrypt(p);
	cout << "加密後的字串為:" << endl;
	DispStr(q);
	p = Unencrypt(q);
	cout <<
 
 "解密後的字串為:" << endl;
	DispStr(p);

	system("pause");
	return 0;
}


SqString encrypt(SqString p){
	int i = 0, j = 0;
	SqString q;		//接收加密對應的字元
	for (i = 0; i <= p.length; i++) {
		j = 0;
		while (p.data[i] != sqStr.data[j] && j < sqStr.length) {
			j++;	//用j控制對應對映位置的字元
		}
		if (j >= sqStr.length)
			q.data[i] = p.data[i];
		else
			q.data[i] = matchStr.data[j];	//將對映的字元賦給字串q的資料
	}
	q.length = p.length;
	return q;
}

SqString Unencrypt(SqString q){
	int i = 0, j;
	SqString p;		//接收解密對應的字元
	for (i = 0; i <= q.length; i++) {
		j = 0;
		while (q.data[i] != matchStr.data[j] && j < matchStr.length) {
			j++;	//用j控制對應解密位置的字元
		}
		if (j >= matchStr.length)
			p.data[i] = q.data[i];
		else
			p.data[i] = sqStr.data[j];		//將解密的字元賦給字串q的資料
	}
	p.length = q.length;
	return p;
}

//SqString.h
#include <iostream>
#define MaxSize 50
using namespace std;

typedef char ElemType;
typedef struct {
	char data[MaxSize];
	int length;
}SqString;

void strAssign(SqString &s, char cstr[]) {
	int i = 0;
	for (i = 0; cstr[i] != '\0'; i++) {
		s.data[i] = cstr[i];
	}
	s.length = i;
}

void DestroyStr(SqString &s) {

}

void DispStr(SqString s) {
	int i;
	if (s.length > 0) {
		for (i = 0; i < s.length; i++) {
			cout << s.data[i];
		}
		cout << endl;
	}
}

執行截圖