float cash=0; void income(float amount); void expend(float amount); void main() { float amount; int choice; while(1) { makechoice: printf("1-Income,2-Expend,3-Balance,4-Exit\n"); printf("Make a choice,please:"); scanf("%d",&choice); if(choice<0||choice>3) { printf("Select error,please re-enter!\n\n"); goto makechoice; } if(choice==0) { printf("Thanks!\n"); break; } if(choice==3) { printf("Current balance:%.2f\n\n",cash); goto makechoice; } printf("Enter the amount of cash:"); scanf("%f",&amount); if(choice==1) income(amount); else expend(amount); printf("\n"); } system("pause"); } void income(float amount) { cash=cash+amount; return cash; }修改成正确代码

请参考下面的代码，其中我对您原有的代码进行了修正：

#include <stdio.h>

float cash = 0;

void income(float amount);
void expend(float amount);

int main() {
    float amount;
    int choice;
    while (1) {
        makechoice:
        printf("1-Income,2-Expend,3-Balance,4-Exit\n");
        printf("Make a choice,please:");
        scanf("%d", &choice);
        if (choice < 1 || choice > 4) {
            printf("Select error,please re-enter!\n\n");
            goto makechoice;
        }
        if (choice == 4) {
            printf("Thanks!\n");
            break;
        }
        if (choice == 3) {
            printf("Current balance:%.2f\n\n", cash);
            goto makechoice;
        }
        printf("Enter the amount of cash:");
        scanf("%f", &amount);
        if (choice == 1)
            income(amount);
        else
            expend(amount);
        printf("\n");
    }
    getchar();
    return 0;
}

void income(float amount) {
    cash += amount;
}

void expend(float amount) {
    if (amount > cash) {
        printf("Insufficient balance!\n");
    } else {
        cash -= amount;
    }
}

在上面的代码中，我对 `main` 函数中的选择逻辑和循环进行了修正，并且修改了 `income` 函数和 `expend` 函数的返回类型和逻辑。需要注意的是，在 `main` 函数的末尾，我添加了一个 `getchar()` 语句，以等待用户在程序退出前按下任意键，以防止程序突然退出。