判断数字字符串并加减法运算函数

大数加减法运算函数，如果2个字符串都是数字，则输入“+”或者“-”进行运算，并输出结果；若其中有一个字符串不是数字，则退出。如：字符串1为123,字符串2为4564，相加结果为4687。

#include
#include
int yunsuan(char a[],char b[])
{
    int len1,len2;
    len1=strlen(a);
    len2=strlen(b);
    for(int i=0;iif(a[i]<'0'||b[i]>'9')
              {
               break;
              }
    }
    for(int i=0;iif(b[i]<'0'||b[i]>'9')
              {
               break;
              }
    }
int main()
{
    char a[80];
    char b[80];
    printf("输入两个字符串：");
    gets(a);
    gets(b);
    yunsuan(a,b);
    char n;
    printf("输入加号或减号：");
    scanf("%c",n);
    for(i=0;i<80;i++)
    {
        if(n='+')
          {
             a[]=a[]+b[];
          }
        else if(n='-')
          {
            a[]=a[]-b[];
          }
    }
    printf("%s",a[]);
}

不知道该怎么写了

代码实现如下，望采纳

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

#define ADD_THRES   (sizeof("4294967295")-2) //两个9位整数相加不会溢出
#define MUL_THRES   (sizeof("65535")-2)    //两个4位整数相乘不会溢出
#define OTH_THRES   (sizeof("4294967295")-1) //两个10位整数相减或相除不会溢出

typedef struct{
  char *leftVal;
  char *rightVal;
  char operator;
}MATH_OPER;

//加法
void Addition(char *leftVal, char *rightVal,
       char *resBuf, unsigned int resbufLen) {
  unsigned int leftLen = strlen(leftVal);
  unsigned int rightLen = strlen(rightVal);

  unsigned char isLeftLonger = (leftLen>=rightLen) ? 1 : 0;
  unsigned int longLen = isLeftLonger ? leftLen : rightLen;
  if(resbufLen < longLen) { //possible carry + string terminator
    fprintf(stderr, "Not enough space for result(cur:%u)!\n", resbufLen);
    return;
  }

  char *longAddend = isLeftLonger ? leftVal : rightVal;
  char *shortAddend = isLeftLonger ? rightVal : leftVal;
  unsigned int diffLen = isLeftLonger ? (leftLen-rightLen) : (rightLen-leftLen);
  //a carry might be generated from adding the most significant digit
  if((leftLen == rightLen) && (leftVal[0]-'0'+rightVal[0]-'0' >= 9))
    resBuf += 1;

  unsigned int carry = 0;
  int i = longLen-1;
  for(; i >= 0; i--) {
    unsigned int leftAddend = longAddend[i] - '0';
    unsigned int rightAddend = (i<diffLen) ? 0 : shortAddend[i-diffLen]-'0';
    unsigned int digitSum = leftAddend + rightAddend + carry;
    resBuf[i] = digitSum % 10 + '0';
    carry = (digitSum >= 10) ? 1 : 0;
  }
  if(carry == 1) {
    resBuf -= 1;
    resBuf[0] = '1';
  }
  else if(leftVal[0]-'0'+rightVal[0]-'0' == 9) {
    resBuf -= 1;
    resBuf[0] = ' '; //fail to generate a carry
  }
}

//减法
void Subtraction(char *leftVal, char *rightVal,
         char *resBuf, unsigned int resbufLen) {
  int cmpVal = strcmp(leftVal, rightVal);
  if(!cmpVal) {
    resBuf[0] = '0';
    return;
  }

  unsigned int leftLen = strlen(leftVal);
  unsigned int rightLen = strlen(rightVal);
  unsigned char isLeftLonger = 0;
  if((leftLen > rightLen) ||       //100-10
    (leftLen == rightLen && cmpVal > 0)) //100-101
    isLeftLonger = 1;
  unsigned int longLen = isLeftLonger ? leftLen : rightLen;
  if(resbufLen <= longLen) { //string terminator
    fprintf(stderr, "Not enough space for result(cur:%u)!\n", resbufLen);
    return;
  }

  char *minuend = isLeftLonger ? leftVal : rightVal;
  char *subtrahend = isLeftLonger ? rightVal : leftVal;
  unsigned int diffLen = isLeftLonger ? (leftLen-rightLen) : (rightLen-leftLen);
  //a borrow will be generated from subtracting the most significant digit
  if(!isLeftLonger) {
    resBuf[0] = '-';
    resBuf += 1;
  }

  unsigned int borrow = 0;
  int i = longLen-1;
  for(; i >= 0; i--)
  {
    unsigned int expanSubtrahend = (i<diffLen) ? '0' : subtrahend[i-diffLen];
    int digitDif = minuend[i] - expanSubtrahend - borrow;
    borrow = (digitDif < 0) ? 1 : 0;
    resBuf[i] = digitDif + borrow*10 + '0';
    //printf("[%d]Dif=%d=%c-%c-%d -> %c\n", i, digitDif, minuend[i], expanSubtrahend, borrow, resBuf[i]);
  }

  //strip leading '0' characters
  int iSrc = 0, iDst = 0, isStripped = 0;
  while(resBuf[iSrc] !='\0') {
    if(isStripped) {
      resBuf[iDst] = resBuf[iSrc];
      iSrc++; iDst++;
    }
    else if(resBuf[iSrc] != '0') {
      resBuf[iDst] = resBuf[iSrc];
      iSrc++; iDst++;
      isStripped = 1;
    }
    else
      iSrc++;
   }
   resBuf[iDst] = '\0';
}
// 测试
#include<assert.h>
#define ASSERT_ADD(_add1, _add2, _sum) do{\
  char resBuf[100] = {0}; \
  Addition(_add1, _add2, resBuf, sizeof(resBuf)); \
  assert(!strcmp(resBuf, _sum)); \
}while(0)
#define ASSERT_SUB(_minu, _subt, _dif) do{\
  char resBuf[100] = {0}; \
  Subtraction(_minu, _subt, resBuf, sizeof(resBuf)); \
  assert(!strcmp(resBuf, _dif)); \
}while(0)
void VerifyOperation(void) {
  ASSERT_ADD("22", "1686486458", "1686486480");
  ASSERT_ADD("8888888888888", "1112", "8888888890000");
  ASSERT_ADD("1234567890123", "1", "1234567890124");
  ASSERT_ADD("1234567890123", "3333333333333", "4567901223456");
  ASSERT_ADD("1234567890123", "9000000000000", "10234567890123");
  ASSERT_ADD("1234567890123", "8867901223000", "10102469113123");
  ASSERT_ADD("1234567890123", "8000000000000", " 9234567890123");
  ASSERT_ADD("1377083362513770833626", "1585054852315850548524", "2962138214829621382150");

  ASSERT_SUB("10012345678890", "1", "10012345678889");
  ASSERT_SUB("1", "10012345678890", "-10012345678889");
  ASSERT_SUB("10012345678890", "10012345678891", "-1");
  ASSERT_SUB("10012345678890", "10012345686945", "-8055");
  ASSERT_SUB("1000000000000", "999999999999", "1");
}